/*******************************************************
Select

(c) 1997 Innobase Oy

Created 12/19/1997 Heikki Tuuri
*******************************************************/

#include "row0sel.h"

#ifdef UNIV_NONINL
#include "row0sel.ic"
#endif

#include "dict0dict.h"
#include "dict0boot.h"
#include "trx0undo.h"
#include "trx0trx.h"
#include "btr0btr.h"
#include "btr0cur.h"
#include "btr0sea.h"
#include "mach0data.h"
#include "que0que.h"
#include "row0upd.h"
#include "row0row.h"
#include "row0vers.h"
#include "rem0cmp.h"
#include "lock0lock.h"
#include "eval0eval.h"
#include "pars0sym.h"
#include "pars0pars.h"
#include "row0mysql.h"
#include "read0read.h"
#include "buf0lru.h"

/* Maximum number of rows to prefetch; MySQL interface has another parameter */
#define SEL_MAX_N_PREFETCH 16

/* Number of rows fetched, after which to start prefetching; MySQL interface
has another parameter */
#define SEL_PREFETCH_LIMIT 1

/* When a select has accessed about this many pages, it returns control back
to que_run_threads: this is to allow canceling runaway queries */

#define SEL_COST_LIMIT 100

/* Flags for search shortcut */
#define SEL_FOUND 0
#define SEL_EXHAUSTED 1
#define SEL_RETRY 2

/************************************************************************
Returns TRUE if the user-defined column values in a secondary index record
are alphabetically the same as the corresponding columns in the clustered
index record.
NOTE: the comparison is NOT done as a binary comparison, but character
fields are compared with collation! */
static ibool row_sel_sec_rec_is_for_clust_rec(
    /*=============================*/
    /* out: TRUE if the secondary
    record is equal to the corresponding
    fields in the clustered record,
    when compared with collation */
    rec_t *sec_rec,            /* in: secondary index record */
    dict_index_t *sec_index,   /* in: secondary index */
    rec_t *clust_rec,          /* in: clustered index record */
    dict_index_t *clust_index) /* in: clustered index */
{
  dict_field_t *ifield;
  dict_col_t *col;
  byte *sec_field;
  ulint sec_len;
  byte *clust_field;
  ulint clust_len;
  ulint n;
  ulint i;
  dtype_t *cur_type;
  mem_heap_t *heap = NULL;
  ulint clust_offsets_[REC_OFFS_NORMAL_SIZE];
  ulint sec_offsets_[REC_OFFS_SMALL_SIZE];
  ulint *clust_offs = clust_offsets_;
  ulint *sec_offs = sec_offsets_;
  ibool is_equal = TRUE;

  *clust_offsets_ = (sizeof clust_offsets_) / sizeof *clust_offsets_;
  *sec_offsets_ = (sizeof sec_offsets_) / sizeof *sec_offsets_;

  clust_offs = rec_get_offsets(clust_rec, clust_index, clust_offs, ULINT_UNDEFINED, &heap);
  sec_offs = rec_get_offsets(sec_rec, sec_index, sec_offs, ULINT_UNDEFINED, &heap);

  n = dict_index_get_n_ordering_defined_by_user(sec_index);

  for (i = 0; i < n; i++)
  {
    ifield = dict_index_get_nth_field(sec_index, i);
    col = dict_field_get_col(ifield);

    clust_field = rec_get_nth_field(clust_rec, clust_offs, dict_col_get_clust_pos(col), &clust_len);
    sec_field = rec_get_nth_field(sec_rec, sec_offs, i, &sec_len);

    if (ifield->prefix_len > 0 && clust_len != UNIV_SQL_NULL)
    {
      cur_type = dict_col_get_type(dict_field_get_col(ifield));

      clust_len = dtype_get_at_most_n_mbchars(cur_type, ifield->prefix_len, clust_len, (char *)clust_field);
    }

    if (0 != cmp_data_data(dict_col_get_type(col), clust_field, clust_len, sec_field, sec_len))
    {
      is_equal = FALSE;
      goto func_exit;
    }
  }

func_exit:
  if (UNIV_LIKELY_NULL(heap))
  {
    mem_heap_free(heap);
  }
  return (is_equal);
}

/*************************************************************************
Creates a select node struct. */

sel_node_t *sel_node_create(
    /*============*/
    /* out, own: select node struct */
    mem_heap_t *heap) /* in: memory heap where created */
{
  sel_node_t *node;

  node = mem_heap_alloc(heap, sizeof(sel_node_t));
  node->common.type = QUE_NODE_SELECT;
  node->state = SEL_NODE_OPEN;

  node->select_will_do_update = FALSE;
  node->latch_mode = BTR_SEARCH_LEAF;

  node->plans = NULL;

  return (node);
}

/*************************************************************************
Frees the memory private to a select node when a query graph is freed,
does not free the heap where the node was originally created. */

void sel_node_free_private(
    /*==================*/
    sel_node_t *node) /* in: select node struct */
{
  ulint i;
  plan_t *plan;

  if (node->plans != NULL)
  {
    for (i = 0; i < node->n_tables; i++)
    {
      plan = sel_node_get_nth_plan(node, i);

      btr_pcur_close(&(plan->pcur));
      btr_pcur_close(&(plan->clust_pcur));

      if (plan->old_vers_heap)
      {
        mem_heap_free(plan->old_vers_heap);
      }
    }
  }
}

/*************************************************************************
Evaluates the values in a select list. If there are aggregate functions,
their argument value is added to the aggregate total. */
UNIV_INLINE
void sel_eval_select_list(
    /*=================*/
    sel_node_t *node) /* in: select node */
{
  que_node_t *exp;

  exp = node->select_list;

  while (exp)
  {
    eval_exp(exp);

    exp = que_node_get_next(exp);
  }
}

/*************************************************************************
Assigns the values in the select list to the possible into-variables in
SELECT ... INTO ... */
UNIV_INLINE
void sel_assign_into_var_values(
    /*=======================*/
    sym_node_t *var,  /* in: first variable in a list of variables */
    sel_node_t *node) /* in: select node */
{
  que_node_t *exp;

  if (var == NULL)
  {
    return;
  }

  exp = node->select_list;

  while (var)
  {
    ut_ad(exp);

    eval_node_copy_val(var->alias, exp);

    exp = que_node_get_next(exp);
    var = que_node_get_next(var);
  }
}

/*************************************************************************
Resets the aggregate value totals in the select list of an aggregate type
query. */
UNIV_INLINE
void sel_reset_aggregate_vals(
    /*=====================*/
    sel_node_t *node) /* in: select node */
{
  func_node_t *func_node;

  ut_ad(node->is_aggregate);

  func_node = node->select_list;

  while (func_node)
  {
    eval_node_set_int_val(func_node, 0);

    func_node = que_node_get_next(func_node);
  }

  node->aggregate_already_fetched = FALSE;
}

/*************************************************************************
Copies the input variable values when an explicit cursor is opened. */
UNIV_INLINE
void row_sel_copy_input_variable_vals(
    /*=============================*/
    sel_node_t *node) /* in: select node */
{
  sym_node_t *var;

  var = UT_LIST_GET_FIRST(node->copy_variables);

  while (var)
  {
    eval_node_copy_val(var, var->alias);

    var->indirection = NULL;

    var = UT_LIST_GET_NEXT(col_var_list, var);
  }
}

/*************************************************************************
Fetches the column values from a record. */
static void row_sel_fetch_columns(
    /*==================*/
    dict_index_t *index,  /* in: record index */
    rec_t *rec,           /* in: record in a clustered or non-clustered
                          index */
    const ulint *offsets, /* in: rec_get_offsets(rec, index) */
    sym_node_t *column)   /* in: first column in a column list, or
                          NULL */
{
  dfield_t *val;
  ulint index_type;
  ulint field_no;
  byte *data;
  ulint len;

  ut_ad(rec_offs_validate(rec, index, offsets));

  if (index->type & DICT_CLUSTERED)
  {
    index_type = SYM_CLUST_FIELD_NO;
  }
  else
  {
    index_type = SYM_SEC_FIELD_NO;
  }

  while (column)
  {
    field_no = column->field_nos[index_type];

    if (field_no != ULINT_UNDEFINED)
    {
      data = rec_get_nth_field(rec, offsets, field_no, &len);

      if (column->copy_val)
      {
        eval_node_copy_and_alloc_val(column, data, len);
      }
      else
      {
        val = que_node_get_val(column);
        dfield_set_data(val, data, len);
      }
    }

    column = UT_LIST_GET_NEXT(col_var_list, column);
  }
}

/*************************************************************************
Allocates a prefetch buffer for a column when prefetch is first time done. */
static void sel_col_prefetch_buf_alloc(
    /*=======================*/
    sym_node_t *column) /* in: symbol table node for a column */
{
  sel_buf_t *sel_buf;
  ulint i;

  ut_ad(que_node_get_type(column) == QUE_NODE_SYMBOL);

  column->prefetch_buf = mem_alloc(SEL_MAX_N_PREFETCH * sizeof(sel_buf_t));
  for (i = 0; i < SEL_MAX_N_PREFETCH; i++)
  {
    sel_buf = column->prefetch_buf + i;

    sel_buf->data = NULL;

    sel_buf->val_buf_size = 0;
  }
}

/*************************************************************************
Frees a prefetch buffer for a column, including the dynamically allocated
memory for data stored there. */

void sel_col_prefetch_buf_free(
    /*======================*/
    sel_buf_t *prefetch_buf) /* in, own: prefetch buffer */
{
  sel_buf_t *sel_buf;
  ulint i;

  for (i = 0; i < SEL_MAX_N_PREFETCH; i++)
  {
    sel_buf = prefetch_buf + i;

    if (sel_buf->val_buf_size > 0)
    {
      mem_free(sel_buf->data);
    }
  }
}

/*************************************************************************
Pops the column values for a prefetched, cached row from the column prefetch
buffers and places them to the val fields in the column nodes. */
static void sel_pop_prefetched_row(
    /*===================*/
    plan_t *plan) /* in: plan node for a table */
{
  sym_node_t *column;
  sel_buf_t *sel_buf;
  dfield_t *val;
  byte *data;
  ulint len;
  ulint val_buf_size;

  ut_ad(plan->n_rows_prefetched > 0);

  column = UT_LIST_GET_FIRST(plan->columns);

  while (column)
  {
    val = que_node_get_val(column);

    if (!column->copy_val)
    {
      /* We did not really push any value for the
      column */

      ut_ad(!column->prefetch_buf);
      ut_ad(que_node_get_val_buf_size(column) == 0);
#ifdef UNIV_DEBUG
      dfield_set_data(val, NULL, 0);
#endif
      goto next_col;
    }

    ut_ad(column->prefetch_buf);

    sel_buf = column->prefetch_buf + plan->first_prefetched;

    data = sel_buf->data;
    len = sel_buf->len;
    val_buf_size = sel_buf->val_buf_size;

    /* We must keep track of the allocated memory for
    column values to be able to free it later: therefore
    we swap the values for sel_buf and val */

    sel_buf->data = dfield_get_data(val);
    sel_buf->len = dfield_get_len(val);
    sel_buf->val_buf_size = que_node_get_val_buf_size(column);

    dfield_set_data(val, data, len);
    que_node_set_val_buf_size(column, val_buf_size);
  next_col:
    column = UT_LIST_GET_NEXT(col_var_list, column);
  }

  plan->n_rows_prefetched--;

  plan->first_prefetched++;
}

/*************************************************************************
Pushes the column values for a prefetched, cached row to the column prefetch
buffers from the val fields in the column nodes. */
UNIV_INLINE
void sel_push_prefetched_row(
    /*====================*/
    plan_t *plan) /* in: plan node for a table */
{
  sym_node_t *column;
  sel_buf_t *sel_buf;
  dfield_t *val;
  byte *data;
  ulint len;
  ulint pos;
  ulint val_buf_size;

  if (plan->n_rows_prefetched == 0)
  {
    pos = 0;
    plan->first_prefetched = 0;
  }
  else
  {
    pos = plan->n_rows_prefetched;

    /* We have the convention that pushing new rows starts only
    after the prefetch stack has been emptied: */

    ut_ad(plan->first_prefetched == 0);
  }

  plan->n_rows_prefetched++;

  ut_ad(pos < SEL_MAX_N_PREFETCH);

  column = UT_LIST_GET_FIRST(plan->columns);

  while (column)
  {
    if (!column->copy_val)
    {
      /* There is no sense to push pointers to database
      page fields when we do not keep latch on the page! */

      goto next_col;
    }

    if (!column->prefetch_buf)
    {
      /* Allocate a new prefetch buffer */

      sel_col_prefetch_buf_alloc(column);
    }

    sel_buf = column->prefetch_buf + pos;

    val = que_node_get_val(column);

    data = dfield_get_data(val);
    len = dfield_get_len(val);
    val_buf_size = que_node_get_val_buf_size(column);

    /* We must keep track of the allocated memory for
    column values to be able to free it later: therefore
    we swap the values for sel_buf and val */

    dfield_set_data(val, sel_buf->data, sel_buf->len);
    que_node_set_val_buf_size(column, sel_buf->val_buf_size);

    sel_buf->data = data;
    sel_buf->len = len;
    sel_buf->val_buf_size = val_buf_size;
  next_col:
    column = UT_LIST_GET_NEXT(col_var_list, column);
  }
}

/*************************************************************************
Builds a previous version of a clustered index record for a consistent read */
static ulint row_sel_build_prev_vers(
    /*====================*/
    /* out: DB_SUCCESS or error code */
    read_view_t *read_view,   /* in: read view */
    plan_t *plan,             /* in: plan node for table */
    rec_t *rec,               /* in: record in a clustered index */
    ulint **offsets,          /* in/out: offsets returned by
                              rec_get_offsets(rec, plan->index) */
    mem_heap_t **offset_heap, /* in/out: memory heap from which
                              the offsets are allocated */
    rec_t **old_vers,         /* out: old version, or NULL if the
                              record does not exist in the view:
                              i.e., it was freshly inserted
                              afterwards */
    mtr_t *mtr)               /* in: mtr */
{
  ulint err;

  if (plan->old_vers_heap)
  {
    mem_heap_empty(plan->old_vers_heap);
  }
  else
  {
    plan->old_vers_heap = mem_heap_create(512);
  }

  err = row_vers_build_for_consistent_read(rec, mtr, plan->index, offsets, read_view, offset_heap, plan->old_vers_heap,
                                           old_vers);
  return (err);
}

/*************************************************************************
Tests the conditions which determine when the index segment we are searching
through has been exhausted. */
UNIV_INLINE
ibool row_sel_test_end_conds(
    /*===================*/
    /* out: TRUE if row passed the tests */
    plan_t *plan) /* in: plan for the table; the column values must
                  already have been retrieved and the right sides of
                  comparisons evaluated */
{
  func_node_t *cond;

  /* All conditions in end_conds are comparisons of a column to an
  expression */

  cond = UT_LIST_GET_FIRST(plan->end_conds);

  while (cond)
  {
    /* Evaluate the left side of the comparison, i.e., get the
    column value if there is an indirection */

    eval_sym(cond->args);

    /* Do the comparison */

    if (!eval_cmp(cond))
    {
      return (FALSE);
    }

    cond = UT_LIST_GET_NEXT(cond_list, cond);
  }

  return (TRUE);
}

/*************************************************************************
Tests the other conditions. */
UNIV_INLINE
ibool row_sel_test_other_conds(
    /*=====================*/
    /* out: TRUE if row passed the tests */
    plan_t *plan) /* in: plan for the table; the column values must
                  already have been retrieved */
{
  func_node_t *cond;

  cond = UT_LIST_GET_FIRST(plan->other_conds);

  while (cond)
  {
    eval_exp(cond);

    if (!eval_node_get_ibool_val(cond))
    {
      return (FALSE);
    }

    cond = UT_LIST_GET_NEXT(cond_list, cond);
  }

  return (TRUE);
}

/*************************************************************************
Retrieves the clustered index record corresponding to a record in a
non-clustered index. Does the necessary locking. */
static ulint row_sel_get_clust_rec(
    /*==================*/
    /* out: DB_SUCCESS or error code */
    sel_node_t *node, /* in: select_node */
    plan_t *plan,     /* in: plan node for table */
    rec_t *rec,       /* in: record in a non-clustered index */
    que_thr_t *thr,   /* in: query thread */
    rec_t **out_rec,  /* out: clustered record or an old version of
                      it, NULL if the old version did not exist
                      in the read view, i.e., it was a fresh
                      inserted version */
    mtr_t *mtr)       /* in: mtr used to get access to the
                      non-clustered record; the same mtr is used to
                      access the clustered index */
{
  dict_index_t *index;
  rec_t *clust_rec;
  rec_t *old_vers;
  ulint err;
  mem_heap_t *heap = NULL;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;
  *offsets_ = (sizeof offsets_) / sizeof *offsets_;

  *out_rec = NULL;

  offsets = rec_get_offsets(rec, btr_pcur_get_btr_cur(&plan->pcur)->index, offsets, ULINT_UNDEFINED, &heap);

  row_build_row_ref_fast(plan->clust_ref, plan->clust_map, rec, offsets);

  index = dict_table_get_first_index(plan->table);

  btr_pcur_open_with_no_init(index, plan->clust_ref, PAGE_CUR_LE, node->latch_mode, &(plan->clust_pcur), 0, mtr);

  clust_rec = btr_pcur_get_rec(&(plan->clust_pcur));

  /* Note: only if the search ends up on a non-infimum record is the
  low_match value the real match to the search tuple */

  if (!page_rec_is_user_rec(clust_rec) || btr_pcur_get_low_match(&(plan->clust_pcur)) < dict_index_get_n_unique(index))
  {
    ut_a(rec_get_deleted_flag(rec, plan->table->comp));
    ut_a(node->read_view);

    /* In a rare case it is possible that no clust rec is found
    for a delete-marked secondary index record: if in row0umod.c
    in row_undo_mod_remove_clust_low() we have already removed
    the clust rec, while purge is still cleaning and removing
    secondary index records associated with earlier versions of
    the clustered index record. In that case we know that the
    clustered index record did not exist in the read view of
    trx. */

    goto func_exit;
  }

  offsets = rec_get_offsets(clust_rec, index, offsets, ULINT_UNDEFINED, &heap);

  if (!node->read_view)
  {
    /* Try to place a lock on the index record */

    /* If innodb_locks_unsafe_for_binlog option is used,
    we lock only the record, i.e., next-key locking is
    not used. */
    ulint lock_type;

    if (srv_locks_unsafe_for_binlog)
    {
      lock_type = LOCK_REC_NOT_GAP;
    }
    else
    {
      lock_type = LOCK_ORDINARY;
    }

    err = lock_clust_rec_read_check_and_lock(0, clust_rec, index, offsets, node->row_lock_mode, lock_type, thr);

    if (err != DB_SUCCESS)
    {
      goto err_exit;
    }
  }
  else
  {
    /* This is a non-locking consistent read: if necessary, fetch
    a previous version of the record */

    old_vers = NULL;

    if (!lock_clust_rec_cons_read_sees(clust_rec, index, offsets, node->read_view))
    {
      err = row_sel_build_prev_vers(node->read_view, plan, clust_rec, &offsets, &heap, &old_vers, mtr);
      if (err != DB_SUCCESS)
      {
        goto err_exit;
      }

      clust_rec = old_vers;

      if (clust_rec == NULL)
      {
        goto func_exit;
      }
    }

    /* If we had to go to an earlier version of row or the
    secondary index record is delete marked, then it may be that
    the secondary index record corresponding to clust_rec
    (or old_vers) is not rec; in that case we must ignore
    such row because in our snapshot rec would not have existed.
    Remember that from rec we cannot see directly which transaction
    id corresponds to it: we have to go to the clustered index
    record. A query where we want to fetch all rows where
    the secondary index value is in some interval would return
    a wrong result if we would not drop rows which we come to
    visit through secondary index records that would not really
    exist in our snapshot. */

    if ((old_vers || rec_get_deleted_flag(rec, plan->table->comp)) &&
        !row_sel_sec_rec_is_for_clust_rec(rec, plan->index, clust_rec, index))
    {
      goto func_exit;
    }
  }

  /* Fetch the columns needed in test conditions */

  row_sel_fetch_columns(index, clust_rec, offsets, UT_LIST_GET_FIRST(plan->columns));
  *out_rec = clust_rec;
func_exit:
  err = DB_SUCCESS;
err_exit:
  if (UNIV_LIKELY_NULL(heap))
  {
    mem_heap_free(heap);
  }
  return (err);
}

/*************************************************************************
Sets a lock on a record. */
UNIV_INLINE
ulint sel_set_rec_lock(
    /*=============*/
    /* out: DB_SUCCESS or error code */
    rec_t *rec,           /* in: record */
    dict_index_t *index,  /* in: index */
    const ulint *offsets, /* in: rec_get_offsets(rec, index) */
    ulint mode,           /* in: lock mode */
    ulint type,           /* in: LOCK_ORDINARY, LOCK_GAP, or LOC_REC_NOT_GAP */
    que_thr_t *thr)       /* in: query thread */
{
  trx_t *trx;
  ulint err;

  trx = thr_get_trx(thr);

  if (UT_LIST_GET_LEN(trx->trx_locks) > 10000)
  {
    if (buf_LRU_buf_pool_running_out())
    {
      return (DB_LOCK_TABLE_FULL);
    }
  }

  if (index->type & DICT_CLUSTERED)
  {
    err = lock_clust_rec_read_check_and_lock(0, rec, index, offsets, mode, type, thr);
  }
  else
  {
    err = lock_sec_rec_read_check_and_lock(0, rec, index, offsets, mode, type, thr);
  }

  return (err);
}

/*************************************************************************
Opens a pcur to a table index. */
static void row_sel_open_pcur(
    /*==============*/
    sel_node_t *node, /* in: select node */
    plan_t *plan,     /* in: table plan */
    ibool search_latch_locked,
    /* in: TRUE if the thread currently
    has the search latch locked in
    s-mode */
    mtr_t *mtr) /* in: mtr */
{
  dict_index_t *index;
  func_node_t *cond;
  que_node_t *exp;
  ulint n_fields;
  ulint has_search_latch = 0; /* RW_S_LATCH or 0 */
  ulint i;

  if (search_latch_locked)
  {
    has_search_latch = RW_S_LATCH;
  }

  index = plan->index;

  /* Calculate the value of the search tuple: the exact match columns
  get their expressions evaluated when we evaluate the right sides of
  end_conds */

  cond = UT_LIST_GET_FIRST(plan->end_conds);

  while (cond)
  {
    eval_exp(que_node_get_next(cond->args));

    cond = UT_LIST_GET_NEXT(cond_list, cond);
  }

  if (plan->tuple)
  {
    n_fields = dtuple_get_n_fields(plan->tuple);

    if (plan->n_exact_match < n_fields)
    {
      /* There is a non-exact match field which must be
      evaluated separately */

      eval_exp(plan->tuple_exps[n_fields - 1]);
    }

    for (i = 0; i < n_fields; i++)
    {
      exp = plan->tuple_exps[i];

      dfield_copy_data(dtuple_get_nth_field(plan->tuple, i), que_node_get_val(exp));
    }

    /* Open pcur to the index */

    btr_pcur_open_with_no_init(index, plan->tuple, plan->mode, node->latch_mode, &(plan->pcur), has_search_latch, mtr);
  }
  else
  {
    /* Open the cursor to the start or the end of the index
    (FALSE: no init) */

    btr_pcur_open_at_index_side(plan->asc, index, node->latch_mode, &(plan->pcur), FALSE, mtr);
  }

  ut_ad(plan->n_rows_prefetched == 0);
  ut_ad(plan->n_rows_fetched == 0);
  ut_ad(plan->cursor_at_end == FALSE);

  plan->pcur_is_open = TRUE;
}

/*************************************************************************
Restores a stored pcur position to a table index. */
static ibool row_sel_restore_pcur_pos(
    /*=====================*/
    /* out: TRUE if the cursor should be moved to
    the next record after we return from this
    function (moved to the previous, in the case
    of a descending cursor) without processing
    again the current cursor record */
    sel_node_t *node, /* in: select node */
    plan_t *plan,     /* in: table plan */
    mtr_t *mtr)       /* in: mtr */
{
  ibool equal_position;
  ulint relative_position;

  ut_ad(!plan->cursor_at_end);

  relative_position = btr_pcur_get_rel_pos(&(plan->pcur));

  equal_position = btr_pcur_restore_position(node->latch_mode, &(plan->pcur), mtr);

  /* If the cursor is traveling upwards, and relative_position is

  (1) BTR_PCUR_BEFORE: this is not allowed, as we did not have a lock
  yet on the successor of the page infimum;
  (2) BTR_PCUR_AFTER: btr_pcur_restore_position placed the cursor on the
  first record GREATER than the predecessor of a page supremum; we have
  not yet processed the cursor record: no need to move the cursor to the
  next record;
  (3) BTR_PCUR_ON: btr_pcur_restore_position placed the cursor on the
  last record LESS or EQUAL to the old stored user record; (a) if
  equal_position is FALSE, this means that the cursor is now on a record
  less than the old user record, and we must move to the next record;
  (b) if equal_position is TRUE, then if
  plan->stored_cursor_rec_processed is TRUE, we must move to the next
  record, else there is no need to move the cursor. */

  if (plan->asc)
  {
    if (relative_position == BTR_PCUR_ON)
    {
      if (equal_position)
      {
        return (plan->stored_cursor_rec_processed);
      }

      return (TRUE);
    }

    ut_ad(relative_position == BTR_PCUR_AFTER || relative_position == BTR_PCUR_AFTER_LAST_IN_TREE);

    return (FALSE);
  }

  /* If the cursor is traveling downwards, and relative_position is

  (1) BTR_PCUR_BEFORE: btr_pcur_restore_position placed the cursor on
  the last record LESS than the successor of a page infimum; we have not
  processed the cursor record: no need to move the cursor;
  (2) BTR_PCUR_AFTER: btr_pcur_restore_position placed the cursor on the
  first record GREATER than the predecessor of a page supremum; we have
  processed the cursor record: we should move the cursor to the previous
  record;
  (3) BTR_PCUR_ON: btr_pcur_restore_position placed the cursor on the
  last record LESS or EQUAL to the old stored user record; (a) if
  equal_position is FALSE, this means that the cursor is now on a record
  less than the old user record, and we need not move to the previous
  record; (b) if equal_position is TRUE, then if
  plan->stored_cursor_rec_processed is TRUE, we must move to the previous
  record, else there is no need to move the cursor. */

  if (relative_position == BTR_PCUR_BEFORE || relative_position == BTR_PCUR_BEFORE_FIRST_IN_TREE)
  {
    return (FALSE);
  }

  if (relative_position == BTR_PCUR_ON)
  {
    if (equal_position)
    {
      return (plan->stored_cursor_rec_processed);
    }

    return (FALSE);
  }

  ut_ad(relative_position == BTR_PCUR_AFTER || relative_position == BTR_PCUR_AFTER_LAST_IN_TREE);

  return (TRUE);
}

/*************************************************************************
Resets a plan cursor to a closed state. */
UNIV_INLINE
void plan_reset_cursor(
    /*==============*/
    plan_t *plan) /* in: plan */
{
  plan->pcur_is_open = FALSE;
  plan->cursor_at_end = FALSE;
  plan->n_rows_fetched = 0;
  plan->n_rows_prefetched = 0;
}

/*************************************************************************
Tries to do a shortcut to fetch a clustered index record with a unique key,
using the hash index if possible (not always). */
static ulint row_sel_try_search_shortcut(
    /*========================*/
    /* out: SEL_FOUND, SEL_EXHAUSTED, SEL_RETRY */
    sel_node_t *node, /* in: select node for a consistent read */
    plan_t *plan,     /* in: plan for a unique search in clustered
                      index */
    mtr_t *mtr)       /* in: mtr */
{
  dict_index_t *index;
  rec_t *rec;
  mem_heap_t *heap = NULL;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;
  ulint ret;
  *offsets_ = (sizeof offsets_) / sizeof *offsets_;

  index = plan->index;

  ut_ad(node->read_view);
  ut_ad(plan->unique_search);
  ut_ad(!plan->must_get_clust);
#ifdef UNIV_SYNC_DEBUG
  ut_ad(rw_lock_own(&btr_search_latch, RW_LOCK_SHARED));
#endif /* UNIV_SYNC_DEBUG */

  row_sel_open_pcur(node, plan, TRUE, mtr);

  rec = btr_pcur_get_rec(&(plan->pcur));

  if (!page_rec_is_user_rec(rec))
  {
    return (SEL_RETRY);
  }

  ut_ad(plan->mode == PAGE_CUR_GE);

  /* As the cursor is now placed on a user record after a search with
  the mode PAGE_CUR_GE, the up_match field in the cursor tells how many
  fields in the user record matched to the search tuple */

  if (btr_pcur_get_up_match(&(plan->pcur)) < plan->n_exact_match)
  {
    return (SEL_EXHAUSTED);
  }

  /* This is a non-locking consistent read: if necessary, fetch
  a previous version of the record */

  offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);

  if (index->type & DICT_CLUSTERED)
  {
    if (!lock_clust_rec_cons_read_sees(rec, index, offsets, node->read_view))
    {
      ret = SEL_RETRY;
      goto func_exit;
    }
  }
  else if (!lock_sec_rec_cons_read_sees(rec, index, node->read_view))
  {
    ret = SEL_RETRY;
    goto func_exit;
  }

  /* Test deleted flag. Fetch the columns needed in test conditions. */

  row_sel_fetch_columns(index, rec, offsets, UT_LIST_GET_FIRST(plan->columns));

  if (rec_get_deleted_flag(rec, plan->table->comp))
  {
    ret = SEL_EXHAUSTED;
    goto func_exit;
  }

  /* Test the rest of search conditions */

  if (!row_sel_test_other_conds(plan))
  {
    ret = SEL_EXHAUSTED;
    goto func_exit;
  }

  ut_ad(plan->pcur.latch_mode == node->latch_mode);

  plan->n_rows_fetched++;
func_exit:
  if (UNIV_LIKELY_NULL(heap))
  {
    mem_heap_free(heap);
  }
  return (SEL_FOUND);
}

/*************************************************************************
Performs a select step. */
static ulint row_sel(
    /*====*/
    /* out: DB_SUCCESS or error code */
    sel_node_t *node, /* in: select node */
    que_thr_t *thr)   /* in: query thread */
{
  dict_index_t *index;
  plan_t *plan;
  mtr_t mtr;
  ibool moved;
  rec_t *rec;
  rec_t *old_vers;
  rec_t *clust_rec;
  ibool search_latch_locked;
  ibool consistent_read;

  /* The following flag becomes TRUE when we are doing a
  consistent read from a non-clustered index and we must look
  at the clustered index to find out the previous delete mark
  state of the non-clustered record: */

  ibool cons_read_requires_clust_rec = FALSE;
  ulint cost_counter = 0;
  ibool cursor_just_opened;
  ibool must_go_to_next;
  ibool leaf_contains_updates = FALSE;
  /* TRUE if select_will_do_update is
  TRUE and the current clustered index
  leaf page has been updated during
  the current mtr: mtr must be committed
  at the same time as the leaf x-latch
  is released */
  ibool mtr_has_extra_clust_latch = FALSE;
  /* TRUE if the search was made using
  a non-clustered index, and we had to
  access the clustered record: now &mtr
  contains a clustered index latch, and
  &mtr must be committed before we move
  to the next non-clustered record */
  ulint found_flag;
  ulint err;
  mem_heap_t *heap = NULL;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;
  *offsets_ = (sizeof offsets_) / sizeof *offsets_;

  ut_ad(thr->run_node == node);

  search_latch_locked = FALSE;

  if (node->read_view)
  {
    /* In consistent reads, we try to do with the hash index and
    not to use the buffer page get. This is to reduce memory bus
    load resulting from semaphore operations. The search latch
    will be s-locked when we access an index with a unique search
    condition, but not locked when we access an index with a
    less selective search condition. */

    consistent_read = TRUE;
  }
  else
  {
    consistent_read = FALSE;
  }

table_loop:
  /* TABLE LOOP
     ----------
  This is the outer major loop in calculating a join. We come here when
  node->fetch_table changes, and after adding a row to aggregate totals
  and, of course, when this function is called. */

  ut_ad(leaf_contains_updates == FALSE);
  ut_ad(mtr_has_extra_clust_latch == FALSE);

  plan = sel_node_get_nth_plan(node, node->fetch_table);
  index = plan->index;

  if (plan->n_rows_prefetched > 0)
  {
    sel_pop_prefetched_row(plan);

    goto next_table_no_mtr;
  }

  if (plan->cursor_at_end)
  {
    /* The cursor has already reached the result set end: no more
    rows to process for this table cursor, as also the prefetch
    stack was empty */

    ut_ad(plan->pcur_is_open);

    goto table_exhausted_no_mtr;
  }

  /* Open a cursor to index, or restore an open cursor position */

  mtr_start(&mtr);

  if (consistent_read && plan->unique_search && !plan->pcur_is_open && !plan->must_get_clust)
  {
    if (!search_latch_locked)
    {
      rw_lock_s_lock(&btr_search_latch);

      search_latch_locked = TRUE;
    }
    else if (btr_search_latch.writer_is_wait_ex)
    {
      /* There is an x-latch request waiting: release the
      s-latch for a moment; as an s-latch here is often
      kept for some 10 searches before being released,
      a waiting x-latch request would block other threads
      from acquiring an s-latch for a long time, lowering
      performance significantly in multiprocessors. */

      rw_lock_s_unlock(&btr_search_latch);
      rw_lock_s_lock(&btr_search_latch);
    }

    found_flag = row_sel_try_search_shortcut(node, plan, &mtr);

    if (found_flag == SEL_FOUND)
    {
      goto next_table;
    }
    else if (found_flag == SEL_EXHAUSTED)
    {
      goto table_exhausted;
    }

    ut_ad(found_flag == SEL_RETRY);

    plan_reset_cursor(plan);

    mtr_commit(&mtr);
    mtr_start(&mtr);
  }

  if (search_latch_locked)
  {
    rw_lock_s_unlock(&btr_search_latch);

    search_latch_locked = FALSE;
  }

  if (!plan->pcur_is_open)
  {
    /* Evaluate the expressions to build the search tuple and
    open the cursor */

    row_sel_open_pcur(node, plan, search_latch_locked, &mtr);

    cursor_just_opened = TRUE;

    /* A new search was made: increment the cost counter */
    cost_counter++;
  }
  else
  {
    /* Restore pcur position to the index */

    must_go_to_next = row_sel_restore_pcur_pos(node, plan, &mtr);

    cursor_just_opened = FALSE;

    if (must_go_to_next)
    {
      /* We have already processed the cursor record: move
      to the next */

      goto next_rec;
    }
  }

rec_loop:
  /* RECORD LOOP
     -----------
  In this loop we use pcur and try to fetch a qualifying row, and
  also fill the prefetch buffer for this table if n_rows_fetched has
  exceeded a threshold. While we are inside this loop, the following
  holds:
  (1) &mtr is started,
  (2) pcur is positioned and open.

  NOTE that if cursor_just_opened is TRUE here, it means that we came
  to this point right after row_sel_open_pcur. */

  ut_ad(mtr_has_extra_clust_latch == FALSE);

  rec = btr_pcur_get_rec(&(plan->pcur));

  /* PHASE 1: Set a lock if specified */

  if (!node->asc && cursor_just_opened && !page_rec_is_supremum(rec))
  {
    /* When we open a cursor for a descending search, we must set
    a next-key lock on the successor record: otherwise it would
    be possible to insert new records next to the cursor position,
    and it might be that these new records should appear in the
    search result set, resulting in the phantom problem. */

    if (!consistent_read)
    {
      /* If innodb_locks_unsafe_for_binlog option is used,
      we lock only the record, i.e., next-key locking is
      not used. */

      rec_t *next_rec = page_rec_get_next(rec);
      ulint lock_type;
      offsets = rec_get_offsets(next_rec, index, offsets, ULINT_UNDEFINED, &heap);

      if (srv_locks_unsafe_for_binlog)
      {
        lock_type = LOCK_REC_NOT_GAP;
      }
      else
      {
        lock_type = LOCK_ORDINARY;
      }

      err = sel_set_rec_lock(next_rec, index, offsets, node->row_lock_mode, lock_type, thr);

      if (err != DB_SUCCESS)
      {
        /* Note that in this case we will store in pcur
        the PREDECESSOR of the record we are waiting
        the lock for */

        goto lock_wait_or_error;
      }
    }
  }

  if (page_rec_is_infimum(rec))
  {
    /* The infimum record on a page cannot be in the result set,
    and neither can a record lock be placed on it: we skip such
    a record. We also increment the cost counter as we may have
    processed yet another page of index. */

    cost_counter++;

    goto next_rec;
  }

  if (!consistent_read)
  {
    /* Try to place a lock on the index record */

    /* If innodb_locks_unsafe_for_binlog option is used,
    we lock only the record, i.e., next-key locking is
    not used. */

    ulint lock_type;
    offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);

    if (srv_locks_unsafe_for_binlog)
    {
      lock_type = LOCK_REC_NOT_GAP;
    }
    else
    {
      lock_type = LOCK_ORDINARY;
    }

    err = sel_set_rec_lock(rec, index, offsets, node->row_lock_mode, lock_type, thr);

    if (err != DB_SUCCESS)
    {
      goto lock_wait_or_error;
    }
  }

  if (page_rec_is_supremum(rec))
  {
    /* A page supremum record cannot be in the result set: skip
    it now when we have placed a possible lock on it */

    goto next_rec;
  }

  ut_ad(page_rec_is_user_rec(rec));

  if (cost_counter > SEL_COST_LIMIT)
  {
    /* Now that we have placed the necessary locks, we can stop
    for a while and store the cursor position; NOTE that if we
    would store the cursor position BEFORE placing a record lock,
    it might happen that the cursor would jump over some records
    that another transaction could meanwhile insert adjacent to
    the cursor: this would result in the phantom problem. */

    goto stop_for_a_while;
  }

  /* PHASE 2: Check a mixed index mix id if needed */

  if (plan->unique_search && cursor_just_opened)
  {
    ut_ad(plan->mode == PAGE_CUR_GE);

    /* As the cursor is now placed on a user record after a search
    with the mode PAGE_CUR_GE, the up_match field in the cursor
    tells how many fields in the user record matched to the search
    tuple */

    if (btr_pcur_get_up_match(&(plan->pcur)) < plan->n_exact_match)
    {
      goto table_exhausted;
    }

    /* Ok, no need to test end_conds or mix id */
  }
  else if (plan->mixed_index)
  {
    /* We have to check if the record in a mixed cluster belongs
    to this table */

    if (!dict_is_mixed_table_rec(plan->table, rec))
    {
      goto next_rec;
    }
  }

  /* We are ready to look at a possible new index entry in the result
  set: the cursor is now placed on a user record */

  /* PHASE 3: Get previous version in a consistent read */

  cons_read_requires_clust_rec = FALSE;
  offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);

  if (consistent_read)
  {
    /* This is a non-locking consistent read: if necessary, fetch
    a previous version of the record */

    if (index->type & DICT_CLUSTERED)
    {
      if (!lock_clust_rec_cons_read_sees(rec, index, offsets, node->read_view))
      {
        err = row_sel_build_prev_vers(node->read_view, plan, rec, &offsets, &heap, &old_vers, &mtr);
        if (err != DB_SUCCESS)
        {
          goto lock_wait_or_error;
        }

        if (old_vers == NULL)
        {
          offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);
          row_sel_fetch_columns(index, rec, offsets, UT_LIST_GET_FIRST(plan->columns));

          if (!row_sel_test_end_conds(plan))
          {
            goto table_exhausted;
          }

          goto next_rec;
        }

        rec = old_vers;
      }
    }
    else if (!lock_sec_rec_cons_read_sees(rec, index, node->read_view))
    {
      cons_read_requires_clust_rec = TRUE;
    }
  }

  /* PHASE 4: Test search end conditions and deleted flag */

  /* Fetch the columns needed in test conditions */

  row_sel_fetch_columns(index, rec, offsets, UT_LIST_GET_FIRST(plan->columns));

  /* Test the selection end conditions: these can only contain columns
  which already are found in the index, even though the index might be
  non-clustered */

  if (plan->unique_search && cursor_just_opened)
  {
    /* No test necessary: the test was already made above */
  }
  else if (!row_sel_test_end_conds(plan))
  {
    goto table_exhausted;
  }

  if (rec_get_deleted_flag(rec, plan->table->comp) && !cons_read_requires_clust_rec)
  {
    /* The record is delete marked: we can skip it if this is
    not a consistent read which might see an earlier version
    of a non-clustered index record */

    if (plan->unique_search)
    {
      goto table_exhausted;
    }

    goto next_rec;
  }

  /* PHASE 5: Get the clustered index record, if needed and if we did
  not do the search using the clustered index */

  if (plan->must_get_clust || cons_read_requires_clust_rec)
  {
    /* It was a non-clustered index and we must fetch also the
    clustered index record */

    err = row_sel_get_clust_rec(node, plan, rec, thr, &clust_rec, &mtr);
    mtr_has_extra_clust_latch = TRUE;

    if (err != DB_SUCCESS)
    {
      goto lock_wait_or_error;
    }

    /* Retrieving the clustered record required a search:
    increment the cost counter */

    cost_counter++;

    if (clust_rec == NULL)
    {
      /* The record did not exist in the read view */
      ut_ad(consistent_read);

      goto next_rec;
    }

    if (rec_get_deleted_flag(clust_rec, plan->table->comp))
    {
      /* The record is delete marked: we can skip it */

      goto next_rec;
    }

    if (node->can_get_updated)
    {
      btr_pcur_store_position(&(plan->clust_pcur), &mtr);
    }
  }

  /* PHASE 6: Test the rest of search conditions */

  if (!row_sel_test_other_conds(plan))
  {
    if (plan->unique_search)
    {
      goto table_exhausted;
    }

    goto next_rec;
  }

  /* PHASE 7: We found a new qualifying row for the current table; push
  the row if prefetch is on, or move to the next table in the join */

  plan->n_rows_fetched++;

  ut_ad(plan->pcur.latch_mode == node->latch_mode);

  if (node->select_will_do_update)
  {
    /* This is a searched update and we can do the update in-place,
    saving CPU time */

    row_upd_in_place_in_select(node, thr, &mtr);

    leaf_contains_updates = TRUE;

    /* When the database is in the online backup mode, the number
    of log records for a single mtr should be small: increment the
    cost counter to ensure it */

    cost_counter += 1 + (SEL_COST_LIMIT / 8);

    if (plan->unique_search)
    {
      goto table_exhausted;
    }

    goto next_rec;
  }

  if ((plan->n_rows_fetched <= SEL_PREFETCH_LIMIT) || plan->unique_search || plan->no_prefetch)
  {
    /* No prefetch in operation: go to the next table */

    goto next_table;
  }

  sel_push_prefetched_row(plan);

  if (plan->n_rows_prefetched == SEL_MAX_N_PREFETCH)
  {
    /* The prefetch buffer is now full */

    sel_pop_prefetched_row(plan);

    goto next_table;
  }

next_rec:
  ut_ad(!search_latch_locked);

  if (mtr_has_extra_clust_latch)
  {
    /* We must commit &mtr if we are moving to the next
    non-clustered index record, because we could break the
    latching order if we would access a different clustered
    index page right away without releasing the previous. */

    goto commit_mtr_for_a_while;
  }

  if (leaf_contains_updates && btr_pcur_is_after_last_on_page(&(plan->pcur), &mtr))
  {
    /* We must commit &mtr if we are moving to a different page,
    because we have done updates to the x-latched leaf page, and
    the latch would be released in btr_pcur_move_to_next, without
    &mtr getting committed there */

    ut_ad(node->asc);

    goto commit_mtr_for_a_while;
  }

  if (node->asc)
  {
    moved = btr_pcur_move_to_next(&(plan->pcur), &mtr);
  }
  else
  {
    moved = btr_pcur_move_to_prev(&(plan->pcur), &mtr);
  }

  if (!moved)
  {
    goto table_exhausted;
  }

  cursor_just_opened = FALSE;

  /* END OF RECORD LOOP
     ------------------ */
  goto rec_loop;

next_table:
  /* We found a record which satisfies the conditions: we can move to
  the next table or return a row in the result set */

  ut_ad(btr_pcur_is_on_user_rec(&(plan->pcur), &mtr));

  if (plan->unique_search && !node->can_get_updated)
  {
    plan->cursor_at_end = TRUE;
  }
  else
  {
    ut_ad(!search_latch_locked);

    plan->stored_cursor_rec_processed = TRUE;

    btr_pcur_store_position(&(plan->pcur), &mtr);
  }

  mtr_commit(&mtr);

  leaf_contains_updates = FALSE;
  mtr_has_extra_clust_latch = FALSE;

next_table_no_mtr:
  /* If we use 'goto' to this label, it means that the row was popped
  from the prefetched rows stack, and &mtr is already committed */

  if (node->fetch_table + 1 == node->n_tables)
  {
    sel_eval_select_list(node);

    if (node->is_aggregate)
    {
      goto table_loop;
    }

    sel_assign_into_var_values(node->into_list, node);

    thr->run_node = que_node_get_parent(node);

    if (search_latch_locked)
    {
      rw_lock_s_unlock(&btr_search_latch);
    }

    err = DB_SUCCESS;
    goto func_exit;
  }

  node->fetch_table++;

  /* When we move to the next table, we first reset the plan cursor:
  we do not care about resetting it when we backtrack from a table */

  plan_reset_cursor(sel_node_get_nth_plan(node, node->fetch_table));

  goto table_loop;

table_exhausted:
  /* The table cursor pcur reached the result set end: backtrack to the
  previous table in the join if we do not have cached prefetched rows */

  plan->cursor_at_end = TRUE;

  mtr_commit(&mtr);

  leaf_contains_updates = FALSE;
  mtr_has_extra_clust_latch = FALSE;

  if (plan->n_rows_prefetched > 0)
  {
    /* The table became exhausted during a prefetch */

    sel_pop_prefetched_row(plan);

    goto next_table_no_mtr;
  }

table_exhausted_no_mtr:
  if (node->fetch_table == 0)
  {
    err = DB_SUCCESS;

    if (node->is_aggregate && !node->aggregate_already_fetched)
    {
      node->aggregate_already_fetched = TRUE;

      sel_assign_into_var_values(node->into_list, node);

      thr->run_node = que_node_get_parent(node);

      if (search_latch_locked)
      {
        rw_lock_s_unlock(&btr_search_latch);
      }

      goto func_exit;
    }

    node->state = SEL_NODE_NO_MORE_ROWS;

    thr->run_node = que_node_get_parent(node);

    if (search_latch_locked)
    {
      rw_lock_s_unlock(&btr_search_latch);
    }

    goto func_exit;
  }

  node->fetch_table--;

  goto table_loop;

stop_for_a_while:
  /* Return control for a while to que_run_threads, so that runaway
  queries can be canceled. NOTE that when we come here, we must, in a
  locking read, have placed the necessary (possibly waiting request)
  record lock on the cursor record or its successor: when we reposition
  the cursor, this record lock guarantees that nobody can meanwhile have
  inserted new records which should have appeared in the result set,
  which would result in the phantom problem. */

  ut_ad(!search_latch_locked);

  plan->stored_cursor_rec_processed = FALSE;
  btr_pcur_store_position(&(plan->pcur), &mtr);

  mtr_commit(&mtr);

  ut_ad(sync_thread_levels_empty_gen(TRUE));
  err = DB_SUCCESS;
  goto func_exit;

commit_mtr_for_a_while:
  /* Stores the cursor position and commits &mtr; this is used if
  &mtr may contain latches which would break the latching order if
  &mtr would not be committed and the latches released. */

  plan->stored_cursor_rec_processed = TRUE;

  ut_ad(!search_latch_locked);
  btr_pcur_store_position(&(plan->pcur), &mtr);

  mtr_commit(&mtr);

  leaf_contains_updates = FALSE;
  mtr_has_extra_clust_latch = FALSE;

  ut_ad(sync_thread_levels_empty_gen(TRUE));

  goto table_loop;

lock_wait_or_error:
  /* See the note at stop_for_a_while: the same holds for this case */

  ut_ad(!btr_pcur_is_before_first_on_page(&(plan->pcur), &mtr) || !node->asc);
  ut_ad(!search_latch_locked);

  plan->stored_cursor_rec_processed = FALSE;
  btr_pcur_store_position(&(plan->pcur), &mtr);

  mtr_commit(&mtr);

  ut_ad(sync_thread_levels_empty_gen(TRUE));

func_exit:
  if (UNIV_LIKELY_NULL(heap))
  {
    mem_heap_free(heap);
  }
  return (err);
}

/**************************************************************************
Performs a select step. This is a high-level function used in SQL execution
graphs. */

que_thr_t *row_sel_step(
    /*=========*/
    /* out: query thread to run next or NULL */
    que_thr_t *thr) /* in: query thread */
{
  ulint i_lock_mode;
  sym_node_t *table_node;
  sel_node_t *node;
  ulint err;

  ut_ad(thr);

  node = thr->run_node;

  ut_ad(que_node_get_type(node) == QUE_NODE_SELECT);

  /* If this is a new time this node is executed (or when execution
  resumes after wait for a table intention lock), set intention locks
  on the tables, or assign a read view */

  if (node->into_list && (thr->prev_node == que_node_get_parent(node)))
  {
    node->state = SEL_NODE_OPEN;
  }

  if (node->state == SEL_NODE_OPEN)
  {
    /* It may be that the current session has not yet started
    its transaction, or it has been committed: */

    trx_start_if_not_started(thr_get_trx(thr));

    plan_reset_cursor(sel_node_get_nth_plan(node, 0));

    if (node->consistent_read)
    {
      /* Assign a read view for the query */
      node->read_view = trx_assign_read_view(thr_get_trx(thr));
    }
    else
    {
      if (node->set_x_locks)
      {
        i_lock_mode = LOCK_IX;
      }
      else
      {
        i_lock_mode = LOCK_IS;
      }

      table_node = node->table_list;

      while (table_node)
      {
        err = lock_table(0, table_node->table, i_lock_mode, thr);
        if (err != DB_SUCCESS)
        {
          que_thr_handle_error(thr, DB_ERROR, NULL, 0);
          return (NULL);
        }

        table_node = que_node_get_next(table_node);
      }
    }

    /* If this is an explicit cursor, copy stored procedure
    variable values, so that the values cannot change between
    fetches (currently, we copy them also for non-explicit
    cursors) */

    if (node->explicit_cursor && UT_LIST_GET_FIRST(node->copy_variables))
    {
      row_sel_copy_input_variable_vals(node);
    }

    node->state = SEL_NODE_FETCH;
    node->fetch_table = 0;

    if (node->is_aggregate)
    {
      /* Reset the aggregate total values */
      sel_reset_aggregate_vals(node);
    }
  }

  err = row_sel(node, thr);

  /* NOTE! if queries are parallelized, the following assignment may
  have problems; the assignment should be made only if thr is the
  only top-level thr in the graph: */

  thr->graph->last_sel_node = node;

  if (err == DB_SUCCESS)
  {
    /* Ok: do nothing */
  }
  else if (err == DB_LOCK_WAIT)
  {
    return (NULL);
  }
  else
  {
    /* SQL error detected */
    fprintf(stderr, "SQL error %lu\n", (ulong)err);

    que_thr_handle_error(thr, DB_ERROR, NULL, 0);

    return (NULL);
  }

  return (thr);
}

/**************************************************************************
Performs a fetch for a cursor. */

que_thr_t *fetch_step(
    /*=======*/
    /* out: query thread to run next or NULL */
    que_thr_t *thr) /* in: query thread */
{
  sel_node_t *sel_node;
  fetch_node_t *node;

  ut_ad(thr);

  node = thr->run_node;
  sel_node = node->cursor_def;

  ut_ad(que_node_get_type(node) == QUE_NODE_FETCH);

  if (thr->prev_node != que_node_get_parent(node))
  {
    if (sel_node->state != SEL_NODE_NO_MORE_ROWS)
    {
      sel_assign_into_var_values(node->into_list, sel_node);
    }

    thr->run_node = que_node_get_parent(node);

    return (thr);
  }

  /* Make the fetch node the parent of the cursor definition for
  the time of the fetch, so that execution knows to return to this
  fetch node after a row has been selected or we know that there is
  no row left */

  sel_node->common.parent = node;

  if (sel_node->state == SEL_NODE_CLOSED)
  {
    /* SQL error detected */
    fprintf(stderr, "SQL error %lu\n", (ulong)DB_ERROR);

    que_thr_handle_error(thr, DB_ERROR, NULL, 0);

    return (NULL);
  }

  thr->run_node = sel_node;

  return (thr);
}

/***************************************************************
Prints a row in a select result. */

que_thr_t *row_printf_step(
    /*============*/
    /* out: query thread to run next or NULL */
    que_thr_t *thr) /* in: query thread */
{
  row_printf_node_t *node;
  sel_node_t *sel_node;
  que_node_t *arg;

  ut_ad(thr);

  node = thr->run_node;

  sel_node = node->sel_node;

  ut_ad(que_node_get_type(node) == QUE_NODE_ROW_PRINTF);

  if (thr->prev_node == que_node_get_parent(node))
  {
    /* Reset the cursor */
    sel_node->state = SEL_NODE_OPEN;

    /* Fetch next row to print */

    thr->run_node = sel_node;

    return (thr);
  }

  if (sel_node->state != SEL_NODE_FETCH)
  {
    ut_ad(sel_node->state == SEL_NODE_NO_MORE_ROWS);

    /* No more rows to print */

    thr->run_node = que_node_get_parent(node);

    return (thr);
  }

  arg = sel_node->select_list;

  while (arg)
  {
    dfield_print_also_hex(que_node_get_val(arg));

    fputs(" ::: ", stderr);

    arg = que_node_get_next(arg);
  }

  putc('\n', stderr);

  /* Fetch next row to print */

  thr->run_node = sel_node;

  return (thr);
}

/********************************************************************
Converts a key value stored in MySQL format to an Innobase dtuple. The last
field of the key value may be just a prefix of a fixed length field: hence
the parameter key_len. But currently we do not allow search keys where the
last field is only a prefix of the full key field len and print a warning if
such appears. A counterpart of this function is
ha_innobase::store_key_val_for_row() in ha_innodb.cc. */

void row_sel_convert_mysql_key_to_innobase(
    /*==================================*/
    dtuple_t *tuple,     /* in: tuple where to build;
                         NOTE: we assume that the type info
                         in the tuple is already according
                         to index! */
    byte *buf,           /* in: buffer to use in field
                         conversions */
    ulint buf_len,       /* in: buffer length */
    dict_index_t *index, /* in: index of the key value */
    byte *key_ptr,       /* in: MySQL key value */
    ulint key_len,       /* in: MySQL key value length */
    trx_t *trx)          /* in: transaction */
{
  byte *original_buf = buf;
  byte *original_key_ptr = key_ptr;
  dict_field_t *field;
  dfield_t *dfield;
  ulint data_offset;
  ulint data_len;
  ulint data_field_len;
  ibool is_null;
  byte *key_end;
  ulint n_fields = 0;
  ulint type;

  /* For documentation of the key value storage format in MySQL, see
  ha_innobase::store_key_val_for_row() in ha_innodb.cc. */

  key_end = key_ptr + key_len;

  /* Permit us to access any field in the tuple (ULINT_MAX): */

  dtuple_set_n_fields(tuple, ULINT_MAX);

  dfield = dtuple_get_nth_field(tuple, 0);
  field = dict_index_get_nth_field(index, 0);

  if (dfield_get_type(dfield)->mtype == DATA_SYS)
  {
    /* A special case: we are looking for a position in the
    generated clustered index which InnoDB automatically added
    to a table with no primary key: the first and the only
    ordering column is ROW_ID which InnoDB stored to the key_ptr
    buffer. */

    ut_a(key_len == DATA_ROW_ID_LEN);

    dfield_set_data(dfield, key_ptr, DATA_ROW_ID_LEN);

    dtuple_set_n_fields(tuple, 1);

    return;
  }

  while (key_ptr < key_end)
  {
    ut_a(dict_col_get_type(field->col)->mtype == dfield_get_type(dfield)->mtype);

    data_offset = 0;
    is_null = FALSE;

    if (!(dfield_get_type(dfield)->prtype & DATA_NOT_NULL))
    {
      /* The first byte in the field tells if this is
      an SQL NULL value */

      data_offset = 1;

      if (*key_ptr != 0)
      {
        dfield_set_data(dfield, NULL, UNIV_SQL_NULL);

        is_null = TRUE;
      }
    }

    type = dfield_get_type(dfield)->mtype;

    /* Calculate data length and data field total length */

    if (type == DATA_BLOB)
    {
      /* The key field is a column prefix of a BLOB or
      TEXT */

      ut_a(field->prefix_len > 0);

      /* MySQL stores the actual data length to the first 2
      bytes after the optional SQL NULL marker byte. The
      storage format is little-endian, that is, the most
      significant byte at a higher address. In UTF-8, MySQL
      seems to reserve field->prefix_len bytes for
      storing this field in the key value buffer, even
      though the actual value only takes data_len bytes
      from the start. */

      data_len = key_ptr[data_offset] + 256 * key_ptr[data_offset + 1];
      data_field_len = data_offset + 2 + field->prefix_len;

      data_offset += 2;

      /* Now that we know the length, we store the column
      value like it would be a fixed char field */
    }
    else if (field->prefix_len > 0)
    {
      /* Looks like MySQL pads unused end bytes in the
      prefix with space. Therefore, also in UTF-8, it is ok
      to compare with a prefix containing full prefix_len
      bytes, and no need to take at most prefix_len / 3
      UTF-8 characters from the start.
      If the prefix is used as the upper end of a LIKE
      'abc%' query, then MySQL pads the end with chars
      0xff. TODO: in that case does it any harm to compare
      with the full prefix_len bytes. How do characters
      0xff in UTF-8 behave? */

      data_len = field->prefix_len;
      data_field_len = data_offset + data_len;
    }
    else
    {
      data_len = dfield_get_type(dfield)->len;
      data_field_len = data_offset + data_len;
    }

    if (dtype_get_mysql_type(dfield_get_type(dfield)) == DATA_MYSQL_TRUE_VARCHAR &&
        dfield_get_type(dfield)->mtype != DATA_INT)
    {
      /* In a MySQL key value format, a true VARCHAR is
      always preceded by 2 bytes of a length field.
      dfield_get_type(dfield)->len returns the maximum
      'payload' len in bytes. That does not include the
      2 bytes that tell the actual data length.

      We added the check != DATA_INT to make sure we do
      not treat MySQL ENUM or SET as a true VARCHAR! */

      data_len += 2;
      data_field_len += 2;
    }

    /* Storing may use at most data_len bytes of buf */

    if (!is_null)
    {
      row_mysql_store_col_in_innobase_format(dfield, buf, FALSE, /* MySQL key value format col */
                                             key_ptr + data_offset, data_len, index->table->comp);
      buf += data_len;
    }

    key_ptr += data_field_len;

    if (key_ptr > key_end)
    {
      /* The last field in key was not a complete key field
      but a prefix of it.

      Print a warning about this! HA_READ_PREFIX_LAST does
      not currently work in InnoDB with partial-field key
      value prefixes. Since MySQL currently uses a padding
      trick to calculate LIKE 'abc%' type queries there
      should never be partial-field prefixes in searches. */

      ut_print_timestamp(stderr);

      fputs(
          "  InnoDB: Warning: using a partial-field key prefix in search.\n"
          "InnoDB: ",
          stderr);
      dict_index_name_print(stderr, trx, index);
      fprintf(stderr,
              ". Last data field length %lu bytes,\n"
              "InnoDB: key ptr now exceeds key end by %lu bytes.\n"
              "InnoDB: Key value in the MySQL format:\n",
              (ulong)data_field_len, (ulong)(key_ptr - key_end));
      fflush(stderr);
      ut_print_buf(stderr, original_key_ptr, key_len);
      fprintf(stderr, "\n");

      if (!is_null)
      {
        dfield->len -= (ulint)(key_ptr - key_end);
      }
    }

    n_fields++;
    field++;
    dfield++;
  }

  ut_a(buf <= original_buf + buf_len);

  /* We set the length of tuple to n_fields: we assume that the memory
  area allocated for it is big enough (usually bigger than n_fields). */

  dtuple_set_n_fields(tuple, n_fields);
}

/******************************************************************
Stores the row id to the prebuilt struct. */
static void row_sel_store_row_id_to_prebuilt(
    /*=============================*/
    row_prebuilt_t *prebuilt, /* in: prebuilt */
    rec_t *index_rec,         /* in: record */
    dict_index_t *index,      /* in: index of the record */
    const ulint *offsets)     /* in: rec_get_offsets
                              (index_rec, index) */
{
  byte *data;
  ulint len;

  ut_ad(rec_offs_validate(index_rec, index, offsets));

  data = rec_get_nth_field(index_rec, offsets, dict_index_get_sys_col_pos(index, DATA_ROW_ID), &len);

  if (len != DATA_ROW_ID_LEN)
  {
    fprintf(stderr, "InnoDB: Error: Row id field is wrong length %lu in ", (ulong)len);
    dict_index_name_print(stderr, prebuilt->trx, index);
    fprintf(stderr,
            "\n"
            "InnoDB: Field number %lu, record:\n",
            (ulong)dict_index_get_sys_col_pos(index, DATA_ROW_ID));
    rec_print_new(stderr, index_rec, offsets);
    putc('\n', stderr);
    ut_error;
  }

  ut_memcpy(prebuilt->row_id, data, len);
}

/******************************************************************
Stores a non-SQL-NULL field in the MySQL format. The counterpart of this
function is row_mysql_store_col_in_innobase_format() in row0mysql.c. */
static void row_sel_field_store_in_mysql_format(
    /*================================*/
    byte *dest,                     /* in/out: buffer where to store; NOTE that BLOBs
                                    are not in themselves stored here: the caller must
                                    allocate and copy the BLOB into buffer before, and pass
                                    the pointer to the BLOB in 'data' */
    const mysql_row_templ_t *templ, /* in: MySQL column template.
                    Its following fields are referenced:
                    type, is_unsigned, mysql_col_len, mbminlen, mbmaxlen */
    byte *data,                     /* in: data to store */
    ulint len)                      /* in: length of the data */
{
  byte *ptr;
  byte *field_end;
  byte *pad_ptr;

  ut_ad(len != UNIV_SQL_NULL);

  if (templ->type == DATA_INT)
  {
    /* Convert integer data from Innobase to a little-endian
    format, sign bit restored to normal */

    ptr = dest + len;

    for (;;)
    {
      ptr--;
      *ptr = *data;
      if (ptr == dest)
      {
        break;
      }
      data++;
    }

    if (!templ->is_unsigned)
    {
      dest[len - 1] = (byte)(dest[len - 1] ^ 128);
    }

    ut_ad(templ->mysql_col_len == len);
  }
  else if (templ->type == DATA_VARCHAR || templ->type == DATA_VARMYSQL || templ->type == DATA_BINARY)
  {
    field_end = dest + templ->mysql_col_len;

    if (templ->mysql_type == DATA_MYSQL_TRUE_VARCHAR)
    {
      /* This is a >= 5.0.3 type true VARCHAR. Store the
      length of the data to the first byte or the first
      two bytes of dest. */

      dest = row_mysql_store_true_var_len(dest, len, templ->mysql_length_bytes);
    }

    /* Copy the actual data */
    ut_memcpy(dest, data, len);

    /* Pad with trailing spaces. We pad with spaces also the
    unused end of a >= 5.0.3 true VARCHAR column, just in case
    MySQL expects its contents to be deterministic. */

    pad_ptr = dest + len;

    ut_ad(templ->mbminlen <= templ->mbmaxlen);

    /* We handle UCS2 charset strings differently. */
    if (templ->mbminlen == 2)
    {
      /* A space char is two bytes, 0x0020 in UCS2 */

      if (len & 1)
      {
        /* A 0x20 has been stripped from the column.
        Pad it back. */

        if (pad_ptr < field_end)
        {
          *pad_ptr = 0x20;
          pad_ptr++;
        }
      }

      /* Pad the rest of the string with 0x0020 */

      while (pad_ptr < field_end)
      {
        *pad_ptr = 0x00;
        pad_ptr++;
        *pad_ptr = 0x20;
        pad_ptr++;
      }
    }
    else
    {
      ut_ad(templ->mbminlen == 1);
      /* space=0x20 */

      memset(pad_ptr, 0x20, field_end - pad_ptr);
    }
  }
  else if (templ->type == DATA_BLOB)
  {
    /* Store a pointer to the BLOB buffer to dest: the BLOB was
    already copied to the buffer in row_sel_store_mysql_rec */

    row_mysql_store_blob_ref(dest, templ->mysql_col_len, data, len);
  }
  else if (templ->type == DATA_MYSQL)
  {
    memcpy(dest, data, len);

    ut_a(templ->mysql_col_len >= len);
    ut_a(templ->mbmaxlen >= templ->mbminlen);

    ut_a(templ->mbmaxlen > templ->mbminlen || templ->mysql_col_len == len);
    /* The following assertion would fail for old tables
    containing UTF-8 ENUM columns due to Bug #9526. */
    ut_ad(!templ->mbmaxlen || !(templ->mysql_col_len % templ->mbmaxlen));
    ut_a(len * templ->mbmaxlen >= templ->mysql_col_len);

    if (templ->mbminlen != templ->mbmaxlen)
    {
      /* Pad with spaces. This undoes the stripping
      done in row0mysql.ic, function
      row_mysql_store_col_in_innobase_format(). */

      memset(dest + len, 0x20, templ->mysql_col_len - len);
    }
  }
  else
  {
    ut_a(templ->type == DATA_CHAR ||
         templ->type == DATA_FIXBINARY
         /*|| templ->type == DATA_SYS_CHILD
         || templ->type == DATA_SYS*/
         || templ->type == DATA_FLOAT || templ->type == DATA_DOUBLE || templ->type == DATA_DECIMAL);
    ut_ad(templ->mysql_col_len == len);

    memcpy(dest, data, len);
  }
}

/******************************************************************
Convert a row in the Innobase format to a row in the MySQL format.
Note that the template in prebuilt may advise us to copy only a few
columns to mysql_rec, other columns are left blank. All columns may not
be needed in the query. */
static ibool row_sel_store_mysql_rec(
    /*====================*/
    /* out: TRUE if success, FALSE if
    could not allocate memory for a BLOB
    (though we may also assert in that
    case) */
    byte *mysql_rec,          /* out: row in the MySQL format */
    row_prebuilt_t *prebuilt, /* in: prebuilt struct */
    rec_t *rec,               /* in: Innobase record in the index
                              which was described in prebuilt's
                              template */
    const ulint *offsets)     /* in: array returned by
                              rec_get_offsets() */
{
  mysql_row_templ_t *templ;
  mem_heap_t *extern_field_heap = NULL;
  byte *data;
  ulint len;
  ulint i;

  ut_ad(prebuilt->mysql_template);
  ut_ad(rec_offs_validate(rec, NULL, offsets));

  if (UNIV_LIKELY_NULL(prebuilt->blob_heap))
  {
    mem_heap_free(prebuilt->blob_heap);
    prebuilt->blob_heap = NULL;
  }

  for (i = 0; i < prebuilt->n_template; i++)
  {
    templ = prebuilt->mysql_template + i;

    data = rec_get_nth_field(rec, offsets, templ->rec_field_no, &len);

    if (UNIV_UNLIKELY(rec_offs_nth_extern(offsets, templ->rec_field_no)))
    {
      /* Copy an externally stored field to the temporary
      heap */

      ut_a(!prebuilt->trx->has_search_latch);

      extern_field_heap = mem_heap_create(UNIV_PAGE_SIZE);

      /* NOTE: if we are retrieving a big BLOB, we may
      already run out of memory in the next call, which
      causes an assert */

      data = btr_rec_copy_externally_stored_field(rec, offsets, templ->rec_field_no, &len, extern_field_heap);

      ut_a(len != UNIV_SQL_NULL);
    }

    if (len != UNIV_SQL_NULL)
    {
      if (UNIV_UNLIKELY(templ->type == DATA_BLOB))
      {
        ut_a(prebuilt->templ_contains_blob);

        /* A heuristic test that we can allocate the
        memory for a big BLOB. We have a safety margin
        of 1000000 bytes. Since the test takes some
        CPU time, we do not use it for small BLOBs. */

        if (UNIV_UNLIKELY(len > 2000000) && UNIV_UNLIKELY(!ut_test_malloc(len + 1000000)))
        {
          ut_print_timestamp(stderr);
          fprintf(stderr,
                  "  InnoDB: Warning: could not allocate %lu + 1000000 bytes to retrieve\n"
                  "InnoDB: a big column. Table name ",
                  (ulong)len);
          ut_print_name(stderr, prebuilt->trx, prebuilt->table->name);
          putc('\n', stderr);

          if (extern_field_heap)
          {
            mem_heap_free(extern_field_heap);
          }
          return (FALSE);
        }

        /* Copy the BLOB data to the BLOB heap of
        prebuilt */

        if (prebuilt->blob_heap == NULL)
        {
          prebuilt->blob_heap = mem_heap_create(len);
        }

        data = memcpy(mem_heap_alloc(prebuilt->blob_heap, len), data, len);
      }

      row_sel_field_store_in_mysql_format(mysql_rec + templ->mysql_col_offset, templ, data, len);

      /* Cleanup */
      if (extern_field_heap)
      {
        mem_heap_free(extern_field_heap);
        extern_field_heap = NULL;
      }

      if (templ->mysql_null_bit_mask)
      {
        /* It is a nullable column with a non-NULL
        value */
        mysql_rec[templ->mysql_null_byte_offset] &= ~(byte)(templ->mysql_null_bit_mask);
      }
    }
    else
    {
      /* MySQL seems to assume the field for an SQL NULL
      value is set to zero or space. Not taking this into
      account caused seg faults with NULL BLOB fields, and
      bug number 154 in the MySQL bug database: GROUP BY
      and DISTINCT could treat NULL values inequal. */
      int pad_char;

      mysql_rec[templ->mysql_null_byte_offset] |= (byte)(templ->mysql_null_bit_mask);
      switch (templ->type)
      {
        case DATA_VARCHAR:
        case DATA_BINARY:
        case DATA_VARMYSQL:
          if (templ->mysql_type == DATA_MYSQL_TRUE_VARCHAR)
          {
            /* This is a >= 5.0.3 type
            true VARCHAR.  Zero the field. */
            pad_char = 0x00;
            break;
          }
          /* Fall through */
        case DATA_CHAR:
        case DATA_FIXBINARY:
        case DATA_MYSQL:
          /* MySQL pads all string types (except
          BLOB, TEXT and true VARCHAR) with space. */
          if (UNIV_UNLIKELY(templ->mbminlen == 2))
          {
            /* Treat UCS2 as a special case. */
            data = mysql_rec + templ->mysql_col_offset;
            len = templ->mysql_col_len;
            /* There are two UCS2 bytes per char,
            so the length has to be even. */
            ut_a(!(len & 1));
            /* Pad with 0x0020. */
            while (len)
            {
              *data++ = 0x00;
              *data++ = 0x20;
              len -= 2;
            }
            continue;
          }
          pad_char = 0x20;
          break;
        default:
          pad_char = 0x00;
          break;
      }

      ut_ad(!pad_char || templ->mbminlen == 1);
      memset(mysql_rec + templ->mysql_col_offset, pad_char, templ->mysql_col_len);
    }
  }

  return (TRUE);
}

/*************************************************************************
Builds a previous version of a clustered index record for a consistent read */
static ulint row_sel_build_prev_vers_for_mysql(
    /*==============================*/
    /* out: DB_SUCCESS or error code */
    read_view_t *read_view,    /* in: read view */
    dict_index_t *clust_index, /* in: clustered index */
    row_prebuilt_t *prebuilt,  /* in: prebuilt struct */
    rec_t *rec,                /* in: record in a clustered index */
    ulint **offsets,           /* in/out: offsets returned by
                               rec_get_offsets(rec, clust_index) */
    mem_heap_t **offset_heap,  /* in/out: memory heap from which
                               the offsets are allocated */
    rec_t **old_vers,          /* out: old version, or NULL if the
                               record does not exist in the view:
                               i.e., it was freshly inserted
                               afterwards */
    mtr_t *mtr)                /* in: mtr */
{
  ulint err;

  if (prebuilt->old_vers_heap)
  {
    mem_heap_empty(prebuilt->old_vers_heap);
  }
  else
  {
    prebuilt->old_vers_heap = mem_heap_create(200);
  }

  err = row_vers_build_for_consistent_read(rec, mtr, clust_index, offsets, read_view, offset_heap,
                                           prebuilt->old_vers_heap, old_vers);
  return (err);
}

/*************************************************************************
Retrieves the clustered index record corresponding to a record in a
non-clustered index. Does the necessary locking. Used in the MySQL
interface. */
static ulint row_sel_get_clust_rec_for_mysql(
    /*============================*/
    /* out: DB_SUCCESS or error code */
    row_prebuilt_t *prebuilt, /* in: prebuilt struct in the handle */
    dict_index_t *sec_index,  /* in: secondary index where rec resides */
    rec_t *rec,               /* in: record in a non-clustered index; if
                              this is a locking read, then rec is not
                              allowed to be delete-marked, and that would
                              not make sense either */
    que_thr_t *thr,           /* in: query thread */
    rec_t **out_rec,          /* out: clustered record or an old version of
                              it, NULL if the old version did not exist
                              in the read view, i.e., it was a fresh
                              inserted version */
    ulint **offsets,          /* out: offsets returned by
                              rec_get_offsets(out_rec, clust_index) */
    mem_heap_t **offset_heap, /* in/out: memory heap from which
                          the offsets are allocated */
    mtr_t *mtr)               /* in: mtr used to get access to the
                              non-clustered record; the same mtr is used to
                              access the clustered index */
{
  dict_index_t *clust_index;
  rec_t *clust_rec;
  rec_t *old_vers;
  ulint err;
  trx_t *trx;

  *out_rec = NULL;
  trx = thr_get_trx(thr);

  row_build_row_ref_in_tuple(prebuilt->clust_ref, sec_index, rec, trx);

  clust_index = dict_table_get_first_index(sec_index->table);

  btr_pcur_open_with_no_init(clust_index, prebuilt->clust_ref, PAGE_CUR_LE, BTR_SEARCH_LEAF, prebuilt->clust_pcur, 0,
                             mtr);

  clust_rec = btr_pcur_get_rec(prebuilt->clust_pcur);

  prebuilt->clust_pcur->trx_if_known = trx;

  /* Note: only if the search ends up on a non-infimum record is the
  low_match value the real match to the search tuple */

  if (!page_rec_is_user_rec(clust_rec) ||
      btr_pcur_get_low_match(prebuilt->clust_pcur) < dict_index_get_n_unique(clust_index))
  {
    /* In a rare case it is possible that no clust rec is found
    for a delete-marked secondary index record: if in row0umod.c
    in row_undo_mod_remove_clust_low() we have already removed
    the clust rec, while purge is still cleaning and removing
    secondary index records associated with earlier versions of
    the clustered index record. In that case we know that the
    clustered index record did not exist in the read view of
    trx. */

    if (!rec_get_deleted_flag(rec, sec_index->table->comp) || prebuilt->select_lock_type != LOCK_NONE)
    {
      ut_print_timestamp(stderr);
      fputs(
          "  InnoDB: error clustered record"
          " for sec rec not found\n"
          "InnoDB: ",
          stderr);
      dict_index_name_print(stderr, trx, sec_index);
      fputs(
          "\n"
          "InnoDB: sec index record ",
          stderr);
      rec_print(stderr, rec, sec_index);
      fputs(
          "\n"
          "InnoDB: clust index record ",
          stderr);
      rec_print(stderr, clust_rec, clust_index);
      putc('\n', stderr);
      trx_print(stderr, trx, 600);

      fputs(
          "\n"
          "InnoDB: Submit a detailed bug report to http://bugs.mysql.com\n",
          stderr);
    }

    clust_rec = NULL;

    goto func_exit;
  }

  *offsets = rec_get_offsets(clust_rec, clust_index, *offsets, ULINT_UNDEFINED, offset_heap);

  if (prebuilt->select_lock_type != LOCK_NONE)
  {
    /* Try to place a lock on the index record; we are searching
    the clust rec with a unique condition, hence
    we set a LOCK_REC_NOT_GAP type lock */

    err = lock_clust_rec_read_check_and_lock(0, clust_rec, clust_index, *offsets, prebuilt->select_lock_type,
                                             LOCK_REC_NOT_GAP, thr);
    if (err != DB_SUCCESS)
    {
      goto err_exit;
    }
  }
  else
  {
    /* This is a non-locking consistent read: if necessary, fetch
    a previous version of the record */

    old_vers = NULL;

    /* If the isolation level allows reading of uncommitted data,
    then we never look for an earlier version */

    if (trx->isolation_level > TRX_ISO_READ_UNCOMMITTED &&
        !lock_clust_rec_cons_read_sees(clust_rec, clust_index, *offsets, trx->read_view))
    {
      /* The following call returns 'offsets' associated with
      'old_vers' */
      err = row_sel_build_prev_vers_for_mysql(trx->read_view, clust_index, prebuilt, clust_rec, offsets, offset_heap,
                                              &old_vers, mtr);

      if (err != DB_SUCCESS)
      {
        goto err_exit;
      }

      clust_rec = old_vers;
    }

    /* If we had to go to an earlier version of row or the
    secondary index record is delete marked, then it may be that
    the secondary index record corresponding to clust_rec
    (or old_vers) is not rec; in that case we must ignore
    such row because in our snapshot rec would not have existed.
    Remember that from rec we cannot see directly which transaction
    id corresponds to it: we have to go to the clustered index
    record. A query where we want to fetch all rows where
    the secondary index value is in some interval would return
    a wrong result if we would not drop rows which we come to
    visit through secondary index records that would not really
    exist in our snapshot. */

    if (clust_rec && (old_vers || rec_get_deleted_flag(rec, sec_index->table->comp)) &&
        !row_sel_sec_rec_is_for_clust_rec(rec, sec_index, clust_rec, clust_index))
    {
      clust_rec = NULL;
    }
    else
    {
#ifdef UNIV_SEARCH_DEBUG
      ut_a(clust_rec == NULL || row_sel_sec_rec_is_for_clust_rec(rec, sec_index, clust_rec, clust_index));
#endif
    }
  }

func_exit:
  *out_rec = clust_rec;

  if (prebuilt->select_lock_type == LOCK_X)
  {
    /* We may use the cursor in update: store its position */

    btr_pcur_store_position(prebuilt->clust_pcur, mtr);
  }

  err = DB_SUCCESS;
err_exit:
  return (err);
}

/************************************************************************
Restores cursor position after it has been stored. We have to take into
account that the record cursor was positioned on may have been deleted.
Then we may have to move the cursor one step up or down. */
static ibool sel_restore_position_for_mysql(
    /*===========================*/
    /* out: TRUE if we may need to
    process the record the cursor is
    now positioned on (i.e. we should
    not go to the next record yet) */
    ibool *same_user_rec, /* out: TRUE if we were able to restore
                          the cursor on a user record with the
                          same ordering prefix in in the
                          B-tree index */
    ulint latch_mode,     /* in: latch mode wished in
                          restoration */
    btr_pcur_t *pcur,     /* in: cursor whose position
                          has been stored */
    ibool moves_up,       /* in: TRUE if the cursor moves up
                          in the index */
    mtr_t *mtr)           /* in: mtr; CAUTION: may commit
                          mtr temporarily! */
{
  ibool success;
  ulint relative_position;

  relative_position = pcur->rel_pos;

  success = btr_pcur_restore_position(latch_mode, pcur, mtr);

  *same_user_rec = success;

  if (relative_position == BTR_PCUR_ON)
  {
    if (success)
    {
      return (FALSE);
    }

    if (moves_up)
    {
      btr_pcur_move_to_next(pcur, mtr);
    }

    return (TRUE);
  }

  if (relative_position == BTR_PCUR_AFTER || relative_position == BTR_PCUR_AFTER_LAST_IN_TREE)
  {
    if (moves_up)
    {
      return (TRUE);
    }

    if (btr_pcur_is_on_user_rec(pcur, mtr))
    {
      btr_pcur_move_to_prev(pcur, mtr);
    }

    return (TRUE);
  }

  ut_ad(relative_position == BTR_PCUR_BEFORE || relative_position == BTR_PCUR_BEFORE_FIRST_IN_TREE);

  if (moves_up && btr_pcur_is_on_user_rec(pcur, mtr))
  {
    btr_pcur_move_to_next(pcur, mtr);
  }

  return (TRUE);
}

/************************************************************************
Pops a cached row for MySQL from the fetch cache. */
UNIV_INLINE
void row_sel_pop_cached_row_for_mysql(
    /*=============================*/
    byte *buf,                /* in/out: buffer where to copy the
                              row */
    row_prebuilt_t *prebuilt) /* in: prebuilt struct */
{
  ulint i;
  mysql_row_templ_t *templ;
  byte *cached_rec;
  ut_ad(prebuilt->n_fetch_cached > 0);
  ut_ad(prebuilt->mysql_prefix_len <= prebuilt->mysql_row_len);

  if (UNIV_UNLIKELY(prebuilt->keep_other_fields_on_keyread))
  {
    /* Copy cache record field by field, don't touch fields that
    are not covered by current key */
    cached_rec = prebuilt->fetch_cache[prebuilt->fetch_cache_first];

    for (i = 0; i < prebuilt->n_template; i++)
    {
      templ = prebuilt->mysql_template + i;
      ut_memcpy(buf + templ->mysql_col_offset, cached_rec + templ->mysql_col_offset, templ->mysql_col_len);
      /* Copy NULL bit of the current field from cached_rec
      to buf */
      if (templ->mysql_null_bit_mask)
      {
        buf[templ->mysql_null_byte_offset] ^=
            (buf[templ->mysql_null_byte_offset] ^ cached_rec[templ->mysql_null_byte_offset]) &
            (byte)templ->mysql_null_bit_mask;
      }
    }
  }
  else
  {
    ut_memcpy(buf, prebuilt->fetch_cache[prebuilt->fetch_cache_first], prebuilt->mysql_prefix_len);
  }
  prebuilt->n_fetch_cached--;
  prebuilt->fetch_cache_first++;

  if (prebuilt->n_fetch_cached == 0)
  {
    prebuilt->fetch_cache_first = 0;
  }
}

/************************************************************************
Pushes a row for MySQL to the fetch cache. */
UNIV_INLINE
void row_sel_push_cache_row_for_mysql(
    /*=============================*/
    row_prebuilt_t *prebuilt, /* in: prebuilt struct */
    rec_t *rec,               /* in: record to push */
    const ulint *offsets)     /* in: rec_get_offsets() */
{
  byte *buf;
  ulint i;

  ut_ad(prebuilt->n_fetch_cached < MYSQL_FETCH_CACHE_SIZE);
  ut_ad(rec_offs_validate(rec, NULL, offsets));
  ut_a(!prebuilt->templ_contains_blob);

  if (prebuilt->fetch_cache[0] == NULL)
  {
    /* Allocate memory for the fetch cache */

    for (i = 0; i < MYSQL_FETCH_CACHE_SIZE; i++)
    {
      /* A user has reported memory corruption in these
      buffers in Linux. Put magic numbers there to help
      to track a possible bug. */

      buf = mem_alloc(prebuilt->mysql_row_len + 8);

      prebuilt->fetch_cache[i] = buf + 4;

      mach_write_to_4(buf, ROW_PREBUILT_FETCH_MAGIC_N);
      mach_write_to_4(buf + 4 + prebuilt->mysql_row_len, ROW_PREBUILT_FETCH_MAGIC_N);
    }
  }

  ut_ad(prebuilt->fetch_cache_first == 0);

  if (UNIV_UNLIKELY(!row_sel_store_mysql_rec(prebuilt->fetch_cache[prebuilt->n_fetch_cached], prebuilt, rec, offsets)))
  {
    ut_error;
  }

  prebuilt->n_fetch_cached++;
}

/*************************************************************************
Tries to do a shortcut to fetch a clustered index record with a unique key,
using the hash index if possible (not always). We assume that the search
mode is PAGE_CUR_GE, it is a consistent read, there is a read view in trx,
btr search latch has been locked in S-mode. */
static ulint row_sel_try_search_shortcut_for_mysql(
    /*==================================*/
    /* out: SEL_FOUND, SEL_EXHAUSTED, SEL_RETRY */
    rec_t **out_rec,          /* out: record if found */
    row_prebuilt_t *prebuilt, /* in: prebuilt struct */
    ulint **offsets,          /* in/out: for rec_get_offsets(*out_rec) */
    mem_heap_t **heap,        /* in/out: heap for rec_get_offsets() */
    mtr_t *mtr)               /* in: started mtr */
{
  dict_index_t *index = prebuilt->index;
  dtuple_t *search_tuple = prebuilt->search_tuple;
  btr_pcur_t *pcur = prebuilt->pcur;
  trx_t *trx = prebuilt->trx;
  rec_t *rec;

  ut_ad(index->type & DICT_CLUSTERED);
  ut_ad(!prebuilt->templ_contains_blob);

  btr_pcur_open_with_no_init(index, search_tuple, PAGE_CUR_GE, BTR_SEARCH_LEAF, pcur,
#ifndef UNIV_SEARCH_DEBUG
                             RW_S_LATCH,
#else
                             0,
#endif
                             mtr);
  rec = btr_pcur_get_rec(pcur);

  if (!page_rec_is_user_rec(rec))
  {
    return (SEL_RETRY);
  }

  /* As the cursor is now placed on a user record after a search with
  the mode PAGE_CUR_GE, the up_match field in the cursor tells how many
  fields in the user record matched to the search tuple */

  if (btr_pcur_get_up_match(pcur) < dtuple_get_n_fields(search_tuple))
  {
    return (SEL_EXHAUSTED);
  }

  /* This is a non-locking consistent read: if necessary, fetch
  a previous version of the record */

  *offsets = rec_get_offsets(rec, index, *offsets, ULINT_UNDEFINED, heap);

  if (!lock_clust_rec_cons_read_sees(rec, index, *offsets, trx->read_view))
  {
    return (SEL_RETRY);
  }

  if (rec_get_deleted_flag(rec, index->table->comp))
  {
    return (SEL_EXHAUSTED);
  }

  *out_rec = rec;

  return (SEL_FOUND);
}

/************************************************************************
Searches for rows in the database. This is used in the interface to
MySQL. This function opens a cursor, and also implements fetch next
and fetch prev. NOTE that if we do a search with a full key value
from a unique index (ROW_SEL_EXACT), then we will not store the cursor
position and fetch next or fetch prev must not be tried to the cursor! */

ulint row_search_for_mysql(
    /*=================*/
    /* out: DB_SUCCESS,
    DB_RECORD_NOT_FOUND,
    DB_END_OF_INDEX, DB_DEADLOCK,
    DB_LOCK_TABLE_FULL, DB_CORRUPTION,
    or DB_TOO_BIG_RECORD */
    byte *buf,                /* in/out: buffer for the fetched
                              row in the MySQL format */
    ulint mode,               /* in: search mode PAGE_CUR_L, ... */
    row_prebuilt_t *prebuilt, /* in: prebuilt struct for the
                              table handle; this contains the info
                              of search_tuple, index; if search
                              tuple contains 0 fields then we
                              position the cursor at the start or
                              the end of the index, depending on
                              'mode' */
    ulint match_mode,         /* in: 0 or ROW_SEL_EXACT or
                              ROW_SEL_EXACT_PREFIX */
    ulint direction)          /* in: 0 or ROW_SEL_NEXT or
                              ROW_SEL_PREV; NOTE: if this is != 0,
                              then prebuilt must have a pcur
                              with stored position! In opening of a
                              cursor 'direction' should be 0. */
{
  dict_index_t *index = prebuilt->index;
  ibool comp = index->table->comp;
  dtuple_t *search_tuple = prebuilt->search_tuple;
  btr_pcur_t *pcur = prebuilt->pcur;
  trx_t *trx = prebuilt->trx;
  dict_index_t *clust_index;
  que_thr_t *thr;
  rec_t *rec;
  rec_t *result_rec;
  rec_t *clust_rec;
  rec_t *old_vers;
  ulint err = DB_SUCCESS;
  ibool unique_search = FALSE;
  ibool unique_search_from_clust_index = FALSE;
  ibool mtr_has_extra_clust_latch = FALSE;
  ibool moves_up = FALSE;
  ibool set_also_gap_locks = TRUE;
  /* if the query is a plain
  locking SELECT, and the isolation
  level is <= TRX_ISO_READ_COMMITTED,
  then this is set to FALSE */
#ifdef UNIV_SEARCH_DEBUG
  ulint cnt = 0;
#endif /* UNIV_SEARCH_DEBUG */
  ulint next_offs;
  ibool same_user_rec;
  mtr_t mtr;
  mem_heap_t *heap = NULL;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;

  *offsets_ = (sizeof offsets_) / sizeof *offsets_;

  ut_ad(index && pcur && search_tuple);
  ut_ad(trx->mysql_thread_id == os_thread_get_curr_id());

  if (UNIV_UNLIKELY(prebuilt->table->ibd_file_missing))
  {
    ut_print_timestamp(stderr);
    fprintf(stderr,
            "  InnoDB: Error:\n"
            "InnoDB: MySQL is trying to use a table handle but the .ibd file for\n"
            "InnoDB: table %s does not exist.\n"
            "InnoDB: Have you deleted the .ibd file from the database directory under\n"
            "InnoDB: the MySQL datadir, or have you used DISCARD TABLESPACE?\n"
            "InnoDB: Look from\n"
            "http://dev.mysql.com/doc/mysql/en/InnoDB_troubleshooting_datadict.html\n"
            "InnoDB: how you can resolve the problem.\n",
            prebuilt->table->name);

    return (DB_ERROR);
  }

  if (UNIV_UNLIKELY(prebuilt->magic_n != ROW_PREBUILT_ALLOCATED))
  {
    fprintf(stderr,
            "InnoDB: Error: trying to free a corrupt\n"
            "InnoDB: table handle. Magic n %lu, table name ",
            (ulong)prebuilt->magic_n);
    ut_print_name(stderr, trx, prebuilt->table->name);
    putc('\n', stderr);

    mem_analyze_corruption((byte *)prebuilt);

    ut_error;
  }

  if (trx->n_mysql_tables_in_use == 0 && UNIV_UNLIKELY(prebuilt->select_lock_type == LOCK_NONE))
  {
    /* Note that if MySQL uses an InnoDB temp table that it
    created inside LOCK TABLES, then n_mysql_tables_in_use can
    be zero; in that case select_lock_type is set to LOCK_X in
    ::start_stmt. */

    /* August 19, 2005 by Heikki: temporarily disable this error print until the
    cursor lock count is done correctly. See bugs #12263 and #12456!

                    fputs(
    "InnoDB: Error: MySQL is trying to perform a SELECT\n"
    "InnoDB: but it has not locked any tables in ::external_lock()!\n",
                          stderr);
                    trx_print(stderr, trx, 600);
                    fputc('\n', stderr);
    */
  }

  /*	fprintf(stderr, "Match mode %lu\n search tuple ", (ulong) match_mode);
          dtuple_print(search_tuple);

          fprintf(stderr, "N tables locked %lu\n", trx->mysql_n_tables_locked);
  */
  /*-------------------------------------------------------------*/
  /* PHASE 0: Release a possible s-latch we are holding on the
  adaptive hash index latch if there is someone waiting behind */

  if (UNIV_UNLIKELY(btr_search_latch.writer != RW_LOCK_NOT_LOCKED) && trx->has_search_latch)
  {
    /* There is an x-latch request on the adaptive hash index:
    release the s-latch to reduce starvation and wait for
    BTR_SEA_TIMEOUT rounds before trying to keep it again over
    calls from MySQL */

    rw_lock_s_unlock(&btr_search_latch);
    trx->has_search_latch = FALSE;

    trx->search_latch_timeout = BTR_SEA_TIMEOUT;
  }

  /* Reset the new record lock info if we srv_locks_unsafe_for_binlog
  is set. Then we are able to remove the record locks set here on an
  individual row. */

  if (srv_locks_unsafe_for_binlog && prebuilt->select_lock_type != LOCK_NONE)
  {
    trx_reset_new_rec_lock_info(trx);
  }

  /*-------------------------------------------------------------*/
  /* PHASE 1: Try to pop the row from the prefetch cache */

  if (UNIV_UNLIKELY(direction == 0))
  {
    trx->op_info = "starting index read";

    prebuilt->n_rows_fetched = 0;
    prebuilt->n_fetch_cached = 0;
    prebuilt->fetch_cache_first = 0;

    if (prebuilt->sel_graph == NULL)
    {
      /* Build a dummy select query graph */
      row_prebuild_sel_graph(prebuilt);
    }
  }
  else
  {
    trx->op_info = "fetching rows";

    if (prebuilt->n_rows_fetched == 0)
    {
      prebuilt->fetch_direction = direction;
    }

    if (UNIV_UNLIKELY(direction != prebuilt->fetch_direction))
    {
      if (UNIV_UNLIKELY(prebuilt->n_fetch_cached > 0))
      {
        ut_error;
        /* TODO: scrollable cursor: restore cursor to
        the place of the latest returned row,
        or better: prevent caching for a scroll
        cursor! */
      }

      prebuilt->n_rows_fetched = 0;
      prebuilt->n_fetch_cached = 0;
      prebuilt->fetch_cache_first = 0;
    }
    else if (UNIV_LIKELY(prebuilt->n_fetch_cached > 0))
    {
      row_sel_pop_cached_row_for_mysql(buf, prebuilt);

      prebuilt->n_rows_fetched++;

      srv_n_rows_read++;
      err = DB_SUCCESS;
      goto func_exit;
    }

    if (prebuilt->fetch_cache_first > 0 && prebuilt->fetch_cache_first < MYSQL_FETCH_CACHE_SIZE)
    {
      /* The previous returned row was popped from the fetch
      cache, but the cache was not full at the time of the
      popping: no more rows can exist in the result set */

      err = DB_RECORD_NOT_FOUND;
      goto func_exit;
    }

    prebuilt->n_rows_fetched++;

    if (prebuilt->n_rows_fetched > 1000000000)
    {
      /* Prevent wrap-over */
      prebuilt->n_rows_fetched = 500000000;
    }

    mode = pcur->search_mode;
  }

  /* In a search where at most one record in the index may match, we
  can use a LOCK_REC_NOT_GAP type record lock when locking a non-delete-
  marked matching record.

  Note that in a unique secondary index there may be different delete-
  marked versions of a record where only the primary key values differ:
  thus in a secondary index we must use next-key locks when locking
  delete-marked records. */

  if (match_mode == ROW_SEL_EXACT && index->type & DICT_UNIQUE &&
      dtuple_get_n_fields(search_tuple) == dict_index_get_n_unique(index) &&
      (index->type & DICT_CLUSTERED || !dtuple_contains_null(search_tuple)))
  {
    /* Note above that a UNIQUE secondary index can contain many
    rows with the same key value if one of the columns is the SQL
    null. A clustered index under MySQL can never contain null
    columns because we demand that all the columns in primary key
    are non-null. */

    unique_search = TRUE;

    /* Even if the condition is unique, MySQL seems to try to
    retrieve also a second row if a primary key contains more than
    1 column. Return immediately if this is not a HANDLER
    command. */

    if (UNIV_UNLIKELY(direction != 0 && !prebuilt->used_in_HANDLER))
    {
      err = DB_RECORD_NOT_FOUND;
      goto func_exit;
    }
  }

  mtr_start(&mtr);

  /*-------------------------------------------------------------*/
  /* PHASE 2: Try fast adaptive hash index search if possible */

  /* Next test if this is the special case where we can use the fast
  adaptive hash index to try the search. Since we must release the
  search system latch when we retrieve an externally stored field, we
  cannot use the adaptive hash index in a search in the case the row
  may be long and there may be externally stored fields */

  if (UNIV_UNLIKELY(direction == 0) && unique_search && index->type & DICT_CLUSTERED &&
      !prebuilt->templ_contains_blob && !prebuilt->used_in_HANDLER && (prebuilt->mysql_row_len < UNIV_PAGE_SIZE / 8))
  {
    mode = PAGE_CUR_GE;

    unique_search_from_clust_index = TRUE;

    if (trx->mysql_n_tables_locked == 0 && prebuilt->select_lock_type == LOCK_NONE &&
        trx->isolation_level > TRX_ISO_READ_UNCOMMITTED && trx->read_view)
    {
      /* This is a SELECT query done as a consistent read,
      and the read view has already been allocated:
      let us try a search shortcut through the hash
      index.
      NOTE that we must also test that
      mysql_n_tables_locked == 0, because this might
      also be INSERT INTO ... SELECT ... or
      CREATE TABLE ... SELECT ... . Our algorithm is
      NOT prepared to inserts interleaved with the SELECT,
      and if we try that, we can deadlock on the adaptive
      hash index semaphore! */

#ifndef UNIV_SEARCH_DEBUG
      if (!trx->has_search_latch)
      {
        rw_lock_s_lock(&btr_search_latch);
        trx->has_search_latch = TRUE;
      }
#endif
      switch (row_sel_try_search_shortcut_for_mysql(&rec, prebuilt, &offsets, &heap, &mtr))
      {
        case SEL_FOUND:
#ifdef UNIV_SEARCH_DEBUG
          ut_a(0 == cmp_dtuple_rec(search_tuple, rec, offsets));
#endif
          if (!row_sel_store_mysql_rec(buf, prebuilt, rec, offsets))
          {
            err = DB_TOO_BIG_RECORD;

            /* We let the main loop to do the
            error handling */
            goto shortcut_fails_too_big_rec;
          }

          mtr_commit(&mtr);

          /* ut_print_name(stderr, index->name);
          fputs(" shortcut\n", stderr); */

          srv_n_rows_read++;

          if (trx->search_latch_timeout > 0 && trx->has_search_latch)
          {
            trx->search_latch_timeout--;

            rw_lock_s_unlock(&btr_search_latch);
            trx->has_search_latch = FALSE;
          }

          /* NOTE that we do NOT store the cursor
          position */
          err = DB_SUCCESS;
          goto func_exit;

        case SEL_EXHAUSTED:
          mtr_commit(&mtr);

          /* ut_print_name(stderr, index->name);
          fputs(" record not found 2\n", stderr); */

          if (trx->search_latch_timeout > 0 && trx->has_search_latch)
          {
            trx->search_latch_timeout--;

            rw_lock_s_unlock(&btr_search_latch);
            trx->has_search_latch = FALSE;
          }

          /* NOTE that we do NOT store the cursor
          position */

          err = DB_RECORD_NOT_FOUND;
          goto func_exit;
      }
    shortcut_fails_too_big_rec:
      mtr_commit(&mtr);
      mtr_start(&mtr);
    }
  }

  /*-------------------------------------------------------------*/
  /* PHASE 3: Open or restore index cursor position */

  if (trx->has_search_latch)
  {
    rw_lock_s_unlock(&btr_search_latch);
    trx->has_search_latch = FALSE;
  }

  trx_start_if_not_started(trx);

  if (trx->isolation_level <= TRX_ISO_READ_COMMITTED && prebuilt->select_lock_type != LOCK_NONE && trx->mysql_query_str)
  {
    /* Scan the MySQL query string; check if SELECT is the first
    word there */
    ibool success;

    dict_accept(*trx->mysql_query_str, "SELECT", &success);

    if (success)
    {
      /* It is a plain locking SELECT and the isolation
      level is low: do not lock gaps */

      set_also_gap_locks = FALSE;
    }
  }

  /* Note that if the search mode was GE or G, then the cursor
  naturally moves upward (in fetch next) in alphabetical order,
  otherwise downward */

  if (UNIV_UNLIKELY(direction == 0))
  {
    if (mode == PAGE_CUR_GE || mode == PAGE_CUR_G)
    {
      moves_up = TRUE;
    }
  }
  else if (direction == ROW_SEL_NEXT)
  {
    moves_up = TRUE;
  }

  thr = que_fork_get_first_thr(prebuilt->sel_graph);

  que_thr_move_to_run_state_for_mysql(thr, trx);

  clust_index = dict_table_get_first_index(index->table);

  if (UNIV_LIKELY(direction != 0))
  {
    if (!sel_restore_position_for_mysql(&same_user_rec, BTR_SEARCH_LEAF, pcur, moves_up, &mtr))
    {
      goto next_rec;
    }
  }
  else if (dtuple_get_n_fields(search_tuple) > 0)
  {
    btr_pcur_open_with_no_init(index, search_tuple, mode, BTR_SEARCH_LEAF, pcur, 0, &mtr);

    pcur->trx_if_known = trx;
  }
  else
  {
    if (mode == PAGE_CUR_G)
    {
      btr_pcur_open_at_index_side(TRUE, index, BTR_SEARCH_LEAF, pcur, FALSE, &mtr);
    }
    else if (mode == PAGE_CUR_L)
    {
      btr_pcur_open_at_index_side(FALSE, index, BTR_SEARCH_LEAF, pcur, FALSE, &mtr);
    }
  }

  if (!prebuilt->sql_stat_start)
  {
    /* No need to set an intention lock or assign a read view */

    if (trx->read_view == NULL && prebuilt->select_lock_type == LOCK_NONE)
    {
      fputs(
          "InnoDB: Error: MySQL is trying to perform a consistent read\n"
          "InnoDB: but the read view is not assigned!\n",
          stderr);
      trx_print(stderr, trx, 600);
      fputc('\n', stderr);
      ut_a(0);
    }
  }
  else if (prebuilt->select_lock_type == LOCK_NONE)
  {
    /* This is a consistent read */
    /* Assign a read view for the query */

    trx_assign_read_view(trx);
    prebuilt->sql_stat_start = FALSE;
  }
  else
  {
    ulint lock_mode;
    if (prebuilt->select_lock_type == LOCK_S)
    {
      lock_mode = LOCK_IS;
    }
    else
    {
      lock_mode = LOCK_IX;
    }
    err = lock_table(0, index->table, lock_mode, thr);

    if (err != DB_SUCCESS)
    {
      goto lock_wait_or_error;
    }
    prebuilt->sql_stat_start = FALSE;
  }

rec_loop:
  /*-------------------------------------------------------------*/
  /* PHASE 4: Look for matching records in a loop */

  rec = btr_pcur_get_rec(pcur);
  ut_ad(!!page_rec_is_comp(rec) == comp);
#ifdef UNIV_SEARCH_DEBUG
/*
        fputs("Using ", stderr);
        dict_index_name_print(stderr, index);
        fprintf(stderr, " cnt %lu ; Page no %lu\n", cnt,
                        buf_frame_get_page_no(buf_frame_align(rec)));
        rec_print(rec);
*/
#endif /* UNIV_SEARCH_DEBUG */

  if (page_rec_is_infimum(rec))
  {
    /* The infimum record on a page cannot be in the result set,
    and neither can a record lock be placed on it: we skip such
    a record. */

    goto next_rec;
  }

  if (page_rec_is_supremum(rec))
  {
    if (set_also_gap_locks && !srv_locks_unsafe_for_binlog && prebuilt->select_lock_type != LOCK_NONE)
    {
      /* Try to place a lock on the index record */

      /* If innodb_locks_unsafe_for_binlog option is used,
      we do not lock gaps. Supremum record is really
      a gap and therefore we do not set locks there. */

      offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);
      err = sel_set_rec_lock(rec, index, offsets, prebuilt->select_lock_type, LOCK_ORDINARY, thr);

      if (err != DB_SUCCESS)
      {
        goto lock_wait_or_error;
      }
    }
    /* A page supremum record cannot be in the result set: skip
    it now that we have placed a possible lock on it */

    goto next_rec;
  }

  /*-------------------------------------------------------------*/
  /* Do sanity checks in case our cursor has bumped into page
  corruption */

  if (comp)
  {
    next_offs = rec_get_next_offs(rec, TRUE);
    if (UNIV_UNLIKELY(next_offs < PAGE_NEW_SUPREMUM))
    {
      goto wrong_offs;
    }
  }
  else
  {
    next_offs = rec_get_next_offs(rec, FALSE);
    if (UNIV_UNLIKELY(next_offs < PAGE_OLD_SUPREMUM))
    {
      goto wrong_offs;
    }
  }

  if (UNIV_UNLIKELY(next_offs >= UNIV_PAGE_SIZE - PAGE_DIR))
  {
  wrong_offs:
    if (srv_force_recovery == 0 || moves_up == FALSE)
    {
      ut_print_timestamp(stderr);
      buf_page_print(buf_frame_align(rec));
      fprintf(stderr,
              "\nInnoDB: rec address %p, first buffer frame %p\n"
              "InnoDB: buffer pool high end %p, buf block fix count %lu\n",
              rec, buf_pool->frame_zero, buf_pool->high_end, (ulong)buf_block_align(rec)->buf_fix_count);
      fprintf(stderr,
              "InnoDB: Index corruption: rec offs %lu next offs %lu, page no %lu,\n"
              "InnoDB: ",
              (ulong)ut_align_offset(rec, UNIV_PAGE_SIZE), (ulong)next_offs, (ulong)buf_frame_get_page_no(rec));
      dict_index_name_print(stderr, trx, index);
      fputs(
          ". Run CHECK TABLE. You may need to\n"
          "InnoDB: restore from a backup, or dump + drop + reimport the table.\n",
          stderr);

      err = DB_CORRUPTION;

      goto lock_wait_or_error;
    }
    else
    {
      /* The user may be dumping a corrupt table. Jump
      over the corruption to recover as much as possible. */

      fprintf(stderr,
              "InnoDB: Index corruption: rec offs %lu next offs %lu, page no %lu,\n"
              "InnoDB: ",
              (ulong)ut_align_offset(rec, UNIV_PAGE_SIZE), (ulong)next_offs, (ulong)buf_frame_get_page_no(rec));
      dict_index_name_print(stderr, trx, index);
      fputs(". We try to skip the rest of the page.\n", stderr);

      btr_pcur_move_to_last_on_page(pcur, &mtr);

      goto next_rec;
    }
  }
  /*-------------------------------------------------------------*/

  /* Calculate the 'offsets' associated with 'rec' */

  offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);

  if (UNIV_UNLIKELY(srv_force_recovery > 0))
  {
    if (!rec_validate(rec, offsets) || !btr_index_rec_validate(rec, index, FALSE))
    {
      fprintf(stderr,
              "InnoDB: Index corruption: rec offs %lu next offs %lu, page no %lu,\n"
              "InnoDB: ",
              (ulong)ut_align_offset(rec, UNIV_PAGE_SIZE), (ulong)next_offs, (ulong)buf_frame_get_page_no(rec));
      dict_index_name_print(stderr, trx, index);
      fputs(". We try to skip the record.\n", stderr);

      goto next_rec;
    }
  }

  /* Note that we cannot trust the up_match value in the cursor at this
  place because we can arrive here after moving the cursor! Thus
  we have to recompare rec and search_tuple to determine if they
  match enough. */

  if (match_mode == ROW_SEL_EXACT)
  {
    /* Test if the index record matches completely to search_tuple
    in prebuilt: if not, then we return with DB_RECORD_NOT_FOUND */

    /* fputs("Comparing rec and search tuple\n", stderr); */

    if (0 != cmp_dtuple_rec(search_tuple, rec, offsets))
    {
      if (set_also_gap_locks && !srv_locks_unsafe_for_binlog && prebuilt->select_lock_type != LOCK_NONE)
      {
        /* Try to place a gap lock on the index
        record only if innodb_locks_unsafe_for_binlog
        option is not set */

        err = sel_set_rec_lock(rec, index, offsets, prebuilt->select_lock_type, LOCK_GAP, thr);

        if (err != DB_SUCCESS)
        {
          goto lock_wait_or_error;
        }
      }

      btr_pcur_store_position(pcur, &mtr);

      err = DB_RECORD_NOT_FOUND;
      /* ut_print_name(stderr, index->name);
      fputs(" record not found 3\n", stderr); */

      goto normal_return;
    }
  }
  else if (match_mode == ROW_SEL_EXACT_PREFIX)
  {
    if (!cmp_dtuple_is_prefix_of_rec(search_tuple, rec, offsets))
    {
      if (set_also_gap_locks && !srv_locks_unsafe_for_binlog && prebuilt->select_lock_type != LOCK_NONE)
      {
        /* Try to place a gap lock on the index
        record only if innodb_locks_unsafe_for_binlog
        option is not set */

        err = sel_set_rec_lock(rec, index, offsets, prebuilt->select_lock_type, LOCK_GAP, thr);

        if (err != DB_SUCCESS)
        {
          goto lock_wait_or_error;
        }
      }

      btr_pcur_store_position(pcur, &mtr);

      err = DB_RECORD_NOT_FOUND;
      /* ut_print_name(stderr, index->name);
      fputs(" record not found 4\n", stderr); */

      goto normal_return;
    }
  }

  /* We are ready to look at a possible new index entry in the result
  set: the cursor is now placed on a user record */

  if (prebuilt->select_lock_type != LOCK_NONE)
  {
    /* Try to place a lock on the index record; note that delete
    marked records are a special case in a unique search. If there
    is a non-delete marked record, then it is enough to lock its
    existence with LOCK_REC_NOT_GAP. */

    /* If innodb_locks_unsafe_for_binlog option is used,
    we lock only the record, i.e., next-key locking is
    not used. */

    ulint lock_type;

    if (!set_also_gap_locks || srv_locks_unsafe_for_binlog ||
        (unique_search && !UNIV_UNLIKELY(rec_get_deleted_flag(rec, comp))))
    {
      goto no_gap_lock;
    }
    else
    {
      lock_type = LOCK_ORDINARY;
    }

    /* If we are doing a 'greater or equal than a primary key
    value' search from a clustered index, and we find a record
    that has that exact primary key value, then there is no need
    to lock the gap before the record, because no insert in the
    gap can be in our search range. That is, no phantom row can
    appear that way.

    An example: if col1 is the primary key, the search is WHERE
    col1 >= 100, and we find a record where col1 = 100, then no
    need to lock the gap before that record. */

    if (index == clust_index && mode == PAGE_CUR_GE && direction == 0 &&
        dtuple_get_n_fields_cmp(search_tuple) == dict_index_get_n_unique(index) &&
        0 == cmp_dtuple_rec(search_tuple, rec, offsets))
    {
    no_gap_lock:
      lock_type = LOCK_REC_NOT_GAP;
    }

    err = sel_set_rec_lock(rec, index, offsets, prebuilt->select_lock_type, lock_type, thr);

    if (err != DB_SUCCESS)
    {
      goto lock_wait_or_error;
    }
  }
  else
  {
    /* This is a non-locking consistent read: if necessary, fetch
    a previous version of the record */

    if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED)
    {
      /* Do nothing: we let a non-locking SELECT read the
      latest version of the record */
    }
    else if (index == clust_index)
    {
      /* Fetch a previous version of the row if the current
      one is not visible in the snapshot; if we have a very
      high force recovery level set, we try to avoid crashes
      by skipping this lookup */

      if (UNIV_LIKELY(srv_force_recovery < 5) && !lock_clust_rec_cons_read_sees(rec, index, offsets, trx->read_view))
      {
        /* The following call returns 'offsets'
        associated with 'old_vers' */
        err = row_sel_build_prev_vers_for_mysql(trx->read_view, clust_index, prebuilt, rec, &offsets, &heap, &old_vers,
                                                &mtr);

        if (err != DB_SUCCESS)
        {
          goto lock_wait_or_error;
        }

        if (old_vers == NULL)
        {
          /* The row did not exist yet in
          the read view */

          goto next_rec;
        }

        rec = old_vers;
      }
    }
    else if (!lock_sec_rec_cons_read_sees(rec, index, trx->read_view))
    {
      /* We are looking into a non-clustered index,
      and to get the right version of the record we
      have to look also into the clustered index: this
      is necessary, because we can only get the undo
      information via the clustered index record. */

      ut_ad(index != clust_index);

      goto requires_clust_rec;
    }
  }

  /* NOTE that at this point rec can be an old version of a clustered
  index record built for a consistent read. We cannot assume after this
  point that rec is on a buffer pool page. Functions like
  page_rec_is_comp() cannot be used! */

  if (UNIV_UNLIKELY(rec_get_deleted_flag(rec, comp)))
  {
    /* The record is delete-marked: we can skip it */

    if (srv_locks_unsafe_for_binlog && prebuilt->select_lock_type != LOCK_NONE)
    {
      /* No need to keep a lock on a delete-marked record
      if we do not want to use next-key locking. */

      row_unlock_for_mysql(prebuilt, TRUE);

      trx_reset_new_rec_lock_info(trx);
    }

    goto next_rec;
  }

  /* Get the clustered index record if needed, if we did not do the
  search using the clustered index. */

  if (index != clust_index && prebuilt->need_to_access_clustered)
  {
  requires_clust_rec:
    /* We use a 'goto' to the preceding label if a consistent
    read of a secondary index record requires us to look up old
    versions of the associated clustered index record. */

    ut_ad(rec_offs_validate(rec, index, offsets));

    /* It was a non-clustered index and we must fetch also the
    clustered index record */

    mtr_has_extra_clust_latch = TRUE;

    /* The following call returns 'offsets' associated with
    'clust_rec'. Note that 'clust_rec' can be an old version
    built for a consistent read. */

    err = row_sel_get_clust_rec_for_mysql(prebuilt, index, rec, thr, &clust_rec, &offsets, &heap, &mtr);
    if (err != DB_SUCCESS)
    {
      goto lock_wait_or_error;
    }

    if (clust_rec == NULL)
    {
      /* The record did not exist in the read view */
      ut_ad(prebuilt->select_lock_type == LOCK_NONE);

      goto next_rec;
    }

    if (UNIV_UNLIKELY(rec_get_deleted_flag(clust_rec, comp)))
    {
      /* The record is delete marked: we can skip it */

      if (srv_locks_unsafe_for_binlog && prebuilt->select_lock_type != LOCK_NONE)
      {
        /* No need to keep a lock on a delete-marked
        record if we do not want to use next-key
        locking. */

        row_unlock_for_mysql(prebuilt, TRUE);

        trx_reset_new_rec_lock_info(trx);
      }

      goto next_rec;
    }

    if (prebuilt->need_to_access_clustered)
    {
      result_rec = clust_rec;

      ut_ad(rec_offs_validate(result_rec, clust_index, offsets));
    }
    else
    {
      /* We used 'offsets' for the clust rec, recalculate
      them for 'rec' */
      offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);
      result_rec = rec;
    }
  }
  else
  {
    result_rec = rec;
  }

  /* We found a qualifying record 'result_rec'. At this point,
  'offsets' are associated with 'result_rec'. */

  ut_ad(rec_offs_validate(result_rec, result_rec != rec ? clust_index : index, offsets));

  if ((match_mode == ROW_SEL_EXACT || prebuilt->n_rows_fetched >= MYSQL_FETCH_CACHE_THRESHOLD) &&
      prebuilt->select_lock_type == LOCK_NONE && !prebuilt->templ_contains_blob &&
      !prebuilt->clust_index_was_generated && !prebuilt->used_in_HANDLER &&
      prebuilt->template_type != ROW_MYSQL_DUMMY_TEMPLATE)
  {
    /* Inside an update, for example, we do not cache rows,
    since we may use the cursor position to do the actual
    update, that is why we require ...lock_type == LOCK_NONE.
    Since we keep space in prebuilt only for the BLOBs of
    a single row, we cannot cache rows in the case there
    are BLOBs in the fields to be fetched. In HANDLER we do
    not cache rows because there the cursor is a scrollable
    cursor. */

    row_sel_push_cache_row_for_mysql(prebuilt, result_rec, offsets);
    if (prebuilt->n_fetch_cached == MYSQL_FETCH_CACHE_SIZE)
    {
      goto got_row;
    }

    goto next_rec;
  }
  else
  {
    if (prebuilt->template_type == ROW_MYSQL_DUMMY_TEMPLATE)
    {
      memcpy(buf + 4, result_rec - rec_offs_extra_size(offsets), rec_offs_size(offsets));
      mach_write_to_4(buf, rec_offs_extra_size(offsets) + 4);
    }
    else
    {
      if (!row_sel_store_mysql_rec(buf, prebuilt, result_rec, offsets))
      {
        err = DB_TOO_BIG_RECORD;

        goto lock_wait_or_error;
      }
    }

    if (prebuilt->clust_index_was_generated)
    {
      if (result_rec != rec)
      {
        offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);
      }
      row_sel_store_row_id_to_prebuilt(prebuilt, rec, index, offsets);
    }
  }

  /* From this point on, 'offsets' are invalid. */

got_row:
  /* We have an optimization to save CPU time: if this is a consistent
  read on a unique condition on the clustered index, then we do not
  store the pcur position, because any fetch next or prev will anyway
  return 'end of file'. An exception is the MySQL HANDLER command
  where the user can move the cursor with PREV or NEXT even after
  a unique search. */

  if (!unique_search_from_clust_index || prebuilt->select_lock_type == LOCK_X || prebuilt->used_in_HANDLER)
  {
    /* Inside an update always store the cursor position */

    btr_pcur_store_position(pcur, &mtr);
  }

  err = DB_SUCCESS;

  goto normal_return;

next_rec:
  /*-------------------------------------------------------------*/
  /* PHASE 5: Move the cursor to the next index record */

  if (UNIV_UNLIKELY(mtr_has_extra_clust_latch))
  {
    /* We must commit mtr if we are moving to the next
    non-clustered index record, because we could break the
    latching order if we would access a different clustered
    index page right away without releasing the previous. */

    btr_pcur_store_position(pcur, &mtr);

    mtr_commit(&mtr);
    mtr_has_extra_clust_latch = FALSE;

    mtr_start(&mtr);
    if (sel_restore_position_for_mysql(&same_user_rec, BTR_SEARCH_LEAF, pcur, moves_up, &mtr))
    {
#ifdef UNIV_SEARCH_DEBUG
      cnt++;
#endif /* UNIV_SEARCH_DEBUG */

      goto rec_loop;
    }
  }

  if (moves_up)
  {
    if (UNIV_UNLIKELY(!btr_pcur_move_to_next(pcur, &mtr)))
    {
    not_moved:
      btr_pcur_store_position(pcur, &mtr);

      if (match_mode != 0)
      {
        err = DB_RECORD_NOT_FOUND;
      }
      else
      {
        err = DB_END_OF_INDEX;
      }

      goto normal_return;
    }
  }
  else
  {
    if (UNIV_UNLIKELY(!btr_pcur_move_to_prev(pcur, &mtr)))
    {
      goto not_moved;
    }
  }

#ifdef UNIV_SEARCH_DEBUG
  cnt++;
#endif /* UNIV_SEARCH_DEBUG */

  goto rec_loop;

lock_wait_or_error:
  /*-------------------------------------------------------------*/

  btr_pcur_store_position(pcur, &mtr);

  mtr_commit(&mtr);
  mtr_has_extra_clust_latch = FALSE;

  trx->error_state = err;

  /* The following is a patch for MySQL */

  que_thr_stop_for_mysql(thr);

  thr->lock_state = QUE_THR_LOCK_ROW;

  if (row_mysql_handle_errors(&err, trx, thr, NULL))
  {
    /* It was a lock wait, and it ended */

    thr->lock_state = QUE_THR_LOCK_NOLOCK;
    mtr_start(&mtr);

    sel_restore_position_for_mysql(&same_user_rec, BTR_SEARCH_LEAF, pcur, moves_up, &mtr);
    if (srv_locks_unsafe_for_binlog && !same_user_rec)
    {
      /* Since we were not able to restore the cursor
      on the same user record, we cannot use
      row_unlock_for_mysql() to unlock any records, and
      we must thus reset the new rec lock info. Since
      in lock0lock.c we have blocked the inheriting of gap
      X-locks, we actually do not have any new record locks
      set in this case.

      Note that if we were able to restore on the 'same'
      user record, it is still possible that we were actually
      waiting on a delete-marked record, and meanwhile
      it was removed by purge and inserted again by some
      other user. But that is no problem, because in
      rec_loop we will again try to set a lock, and
      new_rec_lock_info in trx will be right at the end. */

      trx_reset_new_rec_lock_info(trx);
    }

    mode = pcur->search_mode;

    goto rec_loop;
  }

  thr->lock_state = QUE_THR_LOCK_NOLOCK;

#ifdef UNIV_SEARCH_DEBUG
/*	fputs("Using ", stderr);
        dict_index_name_print(stderr, index);
        fprintf(stderr, " cnt %lu ret value %lu err\n", cnt, err); */
#endif /* UNIV_SEARCH_DEBUG */
  goto func_exit;

normal_return:
  /*-------------------------------------------------------------*/
  que_thr_stop_for_mysql_no_error(thr, trx);

  mtr_commit(&mtr);

  if (prebuilt->n_fetch_cached > 0)
  {
    row_sel_pop_cached_row_for_mysql(buf, prebuilt);

    err = DB_SUCCESS;
  }

#ifdef UNIV_SEARCH_DEBUG
/*	fputs("Using ", stderr);
        dict_index_name_print(stderr, index);
        fprintf(stderr, " cnt %lu ret value %lu err\n", cnt, err); */
#endif /* UNIV_SEARCH_DEBUG */
  if (err == DB_SUCCESS)
  {
    srv_n_rows_read++;
  }

func_exit:
  trx->op_info = "";
  if (UNIV_LIKELY_NULL(heap))
  {
    mem_heap_free(heap);
  }
  return (err);
}

/***********************************************************************
Checks if MySQL at the moment is allowed for this table to retrieve a
consistent read result, or store it to the query cache. */

ibool row_search_check_if_query_cache_permitted(
    /*======================================*/
    /* out: TRUE if storing or retrieving
    from the query cache is permitted */
    trx_t *trx,            /* in: transaction object */
    const char *norm_name) /* in: concatenation of database name,
                           '/' char, table name */
{
  dict_table_t *table;
  ibool ret = FALSE;

  table = dict_table_get(norm_name, trx);

  if (table == NULL)
  {
    return (FALSE);
  }

  mutex_enter(&kernel_mutex);

  /* Start the transaction if it is not started yet */

  trx_start_if_not_started_low(trx);

  /* If there are locks on the table or some trx has invalidated the
  cache up to our trx id, then ret = FALSE.
  We do not check what type locks there are on the table, though only
  IX type locks actually would require ret = FALSE. */

  if (UT_LIST_GET_LEN(table->locks) == 0 && ut_dulint_cmp(trx->id, table->query_cache_inv_trx_id) >= 0)
  {
    ret = TRUE;

    /* If the isolation level is high, assign a read view for the
    transaction if it does not yet have one */

    if (trx->isolation_level >= TRX_ISO_REPEATABLE_READ && !trx->read_view)
    {
      trx->read_view = read_view_open_now(trx, trx->global_read_view_heap);
      trx->global_read_view = trx->read_view;
    }
  }

  mutex_exit(&kernel_mutex);

  return (ret);
}
